Discovering Semantic Patterns in Bibliographically Coupled Documents.

ABSTRACT

ISSUES IN DISCOVERING KNOWLEDGE IN BIBLIOGRAPHIC databases are addressed. An example of semantic pattern analysis is used to demonstrate the methodological aspects of knowledge discovery in bibliographic databases. The semantic pattern analysis is based on the keywords selected from the documents grouped by bibliographical coupling. The frequency distribution patterns suggest the existence of a common intellectual base with a wide range of specialties and marginal areas in the antibiotic resistance literature. The resulting values for keyword density per rank show a difference of ten times between the specialty and marginal keyword densities. The possibilities and further studies of incorporating knowledge discovery results into information retrieval are discussed.

INTRODUCTION

Knowledge discovery in databases (KDD) is considered a process of nontrivial extraction of implicit, previously unknown, and potentially useful information (such as knowledge rules, constraints, regularities) from data in databases (Chen, Han, & Yu, 1996, p. 866). Most research on KDD has focused on applications in business operations and well-structured data. Knowledge discovery in textual databases has been underemphasized (Trybula, 1997). Among the limited publications on KD in textual databases, the full-text document data are the primary source of analysis. Lent, Agrawal, and Srikant (1997) developed a patent mining system at IBM for identifying trends in large textual databases over a period of time. They used sequential pattern mining to identify recurring phrases and generate histories of phrases, after which they then extracted phrases that satisfied a specific trend. Discovering associations among the keywords in texts is another area of research in KD in textual databases. Using background knowledge about the relationships of keywords, Feldman and Hirsh (1996) studied associations among the keywords or concepts representing the documents. The knowledge base they built supplies unary or binary relations among the keywords representing the documents. Feldman, Dagan, and Hirsh (1998) developed a system for Knowledge Discovery in Text (KDT) that extracts keywords to represent document contents and allows users to browse a list of keywords that co-occur with another keyword(s) for knowledge discovery purposes.

Mining in full-text documents attempts to extract useful associations and patterns for representing the document content, including clustering, categorization, summarization, and feature extraction. While many studies using data from bibliographic databases were not conducted in terms of KDD or data mining, they nevertheless bear the marks of KDD's techniques and analysis. Such examples can be found in citation and cocitation analysis (Kassler, 1965; Small, 1973; Small & Sweeney, 1985; Braam, Moed, & van Raan, 1991), keyword classifications (Sparck Jones & Jackson, 1970), investigation of indexing similarities between keywords and controlled vocabularies (Shaw, 1990; Qin, in press), and author mapping (Logan & Shaw, 1987). Discovering knowledge through mining textual data in bibliographic databases presents more problems than mining numerical data. One problem is that most fields in a bibliographic database have long character strings--e.g., author name, title, affiliation, journal title, and indexing terms (from both keywords and controlled vocabularies). Such long strings are usually difficult for statistical packages or data mining software to perform computational tasks. Unlike the full-text document source, bibliographic data are semi-structured. Although it may be an advantage over completely unstructured full-text documents, it also creates a challenge for mining tools that the data in the structured fields should not be mixed up when extracting data sets and performing analysis. Linguistic problems (such as singulars and plurals, stems and suffixes) and inconsistencies in abbreviating journal titles and institution names can also be challenging issues in mining bibliographic data. To obtain valid and reliable data for discovering trends and patterns in subject fields and research, data preprocessing and cleansing can become very time-consuming and both labor and intellectually intensive. However, the most challenging issue remains whether there is a chance for information retrieval systems to "be extended to become knowledge discovery systems," or whether "the kinds of record existing in bibliographical and textual databases offer any possibility of analysis in ways similar to those in more structured factual databases" (Vickery, 1997, pp. 119-20).

This study selected a set of bibliographic records as the data source for discovering semantic patterns among the keywords in these records. The purpose of this keyword analysis was to discover if any semantic patterns existed in the keywords extracted from bibliographically coupled documents regarding antibiotic resistance in pneumonia.

Also, if such patterns did exist, how the discovered knowledge about a subject field can be used to improve the effectiveness of knowledge representation and information retrieval. A preliminary test of antibiotic resistance in pneumonia literature found that documents citing the same publication not only co-cited other publications but also contained semantically similar or same keywords in the titles of cited publications. The frequency distributions of these keywords characterized three distinctive strata: a very small number of keywords falling into the highest frequency region, a relatively larger group with moderate occurrences, and a majority of them appearing only once or twice. If the terms occurring most frequently represent the intellectual base in this subject area (Small, 1973; Small & Sweeney, 1985) and the ones with medium occurrences represent the specialties, then the terms occurring least frequently represent the marginal terms. These marginal terms may be the links between the mainstream of the antibiotic resistance research to the less overt but promising research. The citation-semantic analysis is aimed at discovering semantic patterns of the antibiotic resistance literature so that the analysis process and semantic patterns can be programmed into tools that can assist information searchers in building search queries and customizing their postsearch analysis. Specifically, this project studied whether the distribution follows the three strata described earlier, how such distribution can be measured, and to what extent the keywords in these strata reflect the research front in antibiotic resistance. The methods used to preprocess and analyze the data are discussed in detail in the following sections.

RESEARCH DESIGN

The first and most important step in KDD is to clarify what kinds of knowledge are to be discovered, because this decides what types of data or database one needs to work on and what techniques to use for discovering the knowledge anticipated. In general, mining data in any type of database includes association rule generalization, multilevel data characterization, data classification, data clustering, pattern-based similarity search, and mining path traversal patterns (Chen, Han, & Yu, 1996). This project was to identify semantic patterns in antibiotic resistance literature, which would be based on the frequency analysis of keyword occurrences. To achieve this goal, one can obtain a set of working data either by selecting keywords directly from individual records or by obtaining a more coherent pool(s) of source documents by applying a citation restriction such as bibliographical coupling. When the bibliographical coupling method is used to select source documents, at least one similar publication is cited in all the source documents of a bibliographical coupling pool. By this criterion, the documents can be considered coherent in content. Because of this, the keyword data were collected from pools of source documents through bibliographical coupling.

DATA COLLECTION

The Science Citation Index (SCI) database was used to collect data. The following search query was formulated to achieve relative precision and recall:

SELECT (ANTIBIOTIC? (W) RESISTAN?) AND PNEUMONI?

The query was executed in May 1996 and resulted in a total of 360 postings. After ranking by CR (Cited Reference) field, the number of records was reduced to 340 due to the fact that some records did not include references. In Figure 1, these articles are represented by [a.sub.1], [a.sub.2], [a.sub.3], ..., [a.sub.n]. A total of 8,753 publications ([c.sub.1], [c.sub.2], [c.sub.3], ..., [c.sub.k] in Figure 1) were cited in 340 papers. The highest frequency that a paper was cited was seventy-two times, which means the largest pool of source documents identified via bibliographical coupling contained seventy-two articles (see Table 1). The pools with the same number of source documents were treated as the same rank. All thirty-three ranks in this data set were grouped into three categories: 1 through 10 were large pools, those from 11 to 20 the medium, and the rest the small. The first five pools of source documents were selected from each category for extracting keyword data because of the time constraints for the project. Separate keyword files (i.e., [w.sub.1], [w.sub.2], [w.sub.3], ..., [w.sub.j], in Figure 1) were downloaded for each pool of documents.

[Figure 1 ILLUSTRATION OMITTED]

Table 1. TOP 10 MOST FREQUENTLY CITED DOCUMENTS IN ANTIBIOTIC RESISTANCE IN PNEUMONIA LITERATURE

       Frequency of   Author Name and Source
Rank   Being Cited

  1         72        KLUGMAN KP, 1990, V3, P171, CLIN
                      MICROBIOL REV
  2         45        MARTON A, 1991, V163, P542, J INFECT DIS
  3         41        JACOBS MR, 1978, V299, P735, NEW ENGL J MED
  4         38        FENOLL A, 1991, V13, P56, REV INFECT DIS
  5         34        HANSMAN D, 1967, V2, P264, LANCET
  6         33        APPELBAUM PC, 1992, V15, P77, CLIN INFECT
                      DIS
  7         32        SPIKA JS, 1991, V163, P1273, J INFECT DIS
  8         28        PALLARES R, 1987, V317, P18, NEW ENGL J MED
  9         26        APPELBAUM PC, 1987, V6, P367, EUR J CLIN
                      MICRO
  9         26        WARD J, 1981, V3, P254, REV INFECT DIS
 10         25        JORGENSEN JH, 1990, V34, P2075, ANTIMICROB
                      AGE
 10         25        MUNOZ R, 1991, V164, P302, J INFECT DIS
 10         25        PHILIPPON A, 1989, V33, P1131,
                      ANTIMICROB AGEN

DATA PREPROCESSING

The first step in preprocessing is cleaning the downloaded keyword files and converting them into tables. This can be done easily with a word processor's FIND and REPLACE functions. Macros or programs can also be written to read the text files into database tables. Data preprocessed through either way would need to be checked for errors, missing values, and the irregular labels missed by the REPLACE command. The next step is then to assign to keywords the text codes that can be computed by analytic tools (see Appendix). As mentioned earlier, textual data mining faces difficulty in handling long character strings and normalizing terms linguistically. Long strings would not be suitable for calculating frequencies or performing other statistical analysis. The text codes designed for the keywords in this subject field are mnemonic and, in most cases, comprehensible without the help of the original forms. A dictionary or a knowledge base for linking text codes to their keywords can be built for automatic coding. In coding keywords for this data set, a general rule was made to maintain as much of the original form and semantics of the keywords as possible. Other coding rules were set as follows:

* The same codes were assigned to both singular and plural forms of the same keywords, e.g., invit = invitro activity/invitro activities, child = child/children.

* The same codes were assigned to those having the same stem but different suffixes, e.g., pn-r = penicillin-resistance/penicillin-resistant, ther = therapeutic and therapy.

* Key phrases were coded by the noun with its modifying adjective or noun as a modifier, e.g., pnu-k = klebsiella pneumoniae, pnu-r = resistant pnuemoniae, pnu-s = streptococcus pnuemoniae.

* A few keywords that were semantically the same but morphologically different were given the same code for the purpose of joining those with the same meanings. Only two keywords fell into this category in this data set: child was used for coding child, children, infants, and pediatric patients; and 3rdw for third-world and developing-countries.

The text coding process was done semi-manually since building the initial code dictionary often needs human intelligence to analyze and translate a keyword or phrase into an appropriate code. The coding consistency (i.e., the same keyword is given the same code or vice versa throughout the data set) was double checked by sorting the data in the order of keyword and text code and then the order of text code and keyword.

DATA ANALYSIS

Data analysis in KDD processes is associated with data generalization and summarization which "presents the general characteristics or a summarized high-level view over a set of user-specified data in a database" (Chen, Han,& Yu, 1006, p. 866). The semantic patterns of keywords can be generalized from different perspectives--the simple frequency of occurrences and co-occurrences, or the number of unique keywords per rank (frequency), each of which uses a different measure to analyze the data. The simple frequency of occurrences counts how many times a keyword appears in a bibliographic coupling pool. It draws a high-level view of the semantic patterns from keyword frequency distribution. How often a keyword occurred is often decided by the size of the keyword pool. Obviously, the larger a keyword pool is, the more likely it is for a keyword to occur more frequently. When comparing the simple keyword frequency of a large pool of source documents with that of a smaller one, the result can be misleading because of the uneven bases for comparison. A more meaningful and reliable measure would be relative occurrences--i.e., percentage of times that a keyword appears in the total occurrences.

The frequency of co-occurrences is useful for measuring the importance of a keyword in the subject area, but it needs to be used with care. This data set was divided into large, medium, and small groups of source document pools. A complete coordination of all possible co-occurrences would involve those between groups 1 and 2, 1 and 3, 2 and 3, and among all three. Even though a keyword may appear in two or three groups at the same time, its frequency of occurrences may vary greatly in different groups. There were also large variations in the numbers of total ranks or frequencies of keyword occurrences: thirty-three in the large group, twenty-four in the medium, and eleven in the small. These can lead to an invalid comparison for the same keyword with the same rank number but in different groups. For instance, a keyword ranked at eleven in the large group, which was considered high in its group, would have meant the lowest rank in the small group.

To normalize the frequency of occurrences, a measure of keyword density per rank was used. The keyword density per rank can be interpreted as the ratio of the number of unique keywords to the number of ranks at which the unique keywords occurred. It can be expressed in the following formula:

[1] [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

Where D(t) = Average number of keywords [t.sub.1], [t.sub.2], ..., [t.sub.i] per rank,

[r.sub.i] = Number of ranks,

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] = Total number of unique keywords included from ranks 1 through n.

Figure 2 shows how the keyboard density was calculated.

[Figure 2 ILLUSTRATION OMITTED]

This measure eliminates the defects of simple frequency and co-occurrences and focuses on how many unique keywords scatter in a region.

This region is denoted by the frequency rank, and its size can be set according to the distribution shape. In Equation [1], the least possible D(t) is 1, that is, both the number of unique keywords and the number of ranks are the same. For example, three unique keywords were found to have appeared in three different frequencies (or frequency ranks), then 3/3 = 1. The largest possible D(t) can be an infinite in theory, which means that all unique keywords appeared at the same one rank. It is clear that the keyword density will increase as a rank contains more unique keywords.

FINDINGS

Frequency Distribution

There were a total of 2,994 keywords in the fifteen pools of source documents. The number of keywords in the large group (source document pools 1-5) consists of 54.5 percent of the total. The medium group had slightly over 40 percent keywords, and the small group only about 10 percent (see Table 2). The decrease in the number of keywords was mainly due to the decrease in the size of document pools; the average number of keywords (7) per record remained approximately the same for each pool. Nonetheless, the frequency distribution of keywords in all three groups was very similar: a majority of the keywords appeared less than five times in each of the groups; as the occurrences increased, the percentage of keywords decreased (see Figure 3).

[Figure 3 ILLUSTRATION OMITTED]

Table 2. NUMBER OF KEYWORDS IN INDEXING RECORDS FOR THE SOURCE DOCUMENTS IDENTIFIED THROUGH BIBLIOGRAPHICAL COUPLING

Group Size by
Number of       Document   Number of   Number of   Percentage
Documents         Pool     Documents   Keywords

Large              1           72          512        17.1
(Pools of
source             2           45          316        10.6
documents
identified         3           41          291         9.7
through
bibliographic      4           38          273         9.1
coupling)
                   5           34          241         8.0

Medium             6           25          200         6.7

                   7           25          208         7.0

                   8           23          207         7.0

                   9           23          171         5.7

                  10           23          202         6.7

Small             11           11           78         2.6

                  12           11           77         2.6

                  13           10           73         2.4

                  14           10           67         2.2

                  15           10           78         2.6

Total                         401        2,994       100.0

Group Size by
Number of       Cumulative
Documents       Percentage

Large              17.1
(Pools of
source             27.7
documents
identified         37.4
through
bibliographic      46.5
coupling)
                   54.5

Medium             61.2

                   68.2

                   75.2

                   80.9

                   87.6

Small              90.2

                   92.8

                   95.2

                   97.4

                  100.0

Although the percentage of keywords declined dramatically as the group size decreased, all three groups shared the same top three keywords--antibiotic resistance, antimicrobial resistance, and streptococcus-pneumoniae. This suggests that a common "intellectual base" existed among all three groups (see Table 3). The percentage of these three keywords dropped in medium and small groups compared to the large group. A close examination of data revealed that the lower occurrences were caused mainly by fluctuations in individual groups (see Figure 4). Figure 4 suggests that such fluctuations became wider as the group size shrunk to the next level.

[Figure 4 ILLUSTRATION OMITTED]

Table 3. RELATIVE FREQUENCIES OF KEYWORDS IN THE FIRST 25TH PERCENTILES IN THREE GROUPS

Keywords                       Large Group        Medium Group

                            Rank   Rel. freq.   Rank   Rel. freq.

Antibiotic-                    1       7.8         1       6.0
 resistance
Antimicrobial                  2       5.2         2       5.2
 resistance
Streptococcus-                 3       5.1         3       4.0
 pneumoniae
Children/Infants/              4       4.2         6       2.6
 Pediatric patients
Susceptibility                 5       3.7
Infection/infections
Day-care center/                                   7       2.2
 centers
United States                                      5       3.0
Haemophilus-influenza                              4       3.4
3rd-generation
 cephalosporins
Escherichia-co
Mechanically ventilated
 patients
Penicillin-binding protein                         7       2.2

Keywords                       Small Group

                             Rank   Rel. freq.

Antibiotic-                   1        4.6
 resistance
Antimicrobial                 2        3.2
 resistance
Streptococcus-                3        2.9
 pneumoniae
Children/Infants/             4        2.2
 Pediatric patients
Susceptibility                6        1.9
Infection/infections          6        1.9
Day-care center/
 centers
United States                 6        1.9
Haemophilus-influenza
3rd-generation                5        2.1
 cephalosporins
Escherichia-co                6        1.9
Mechanically ventilated       6        1.9
 patients
Penicillin-binding protein

Co-Occurrence of Keywords

In addition to the base keywords, other keywords co-occurred in either all three groups or two of the three. The largest number of keywords (eighty-five) co-occurred in all three groups. Only seven keywords co-occurred in both the large and small groups besides the eighty-five (see Table 4). The number of unique keywords that occurred in only one group was surprisingly similar: 25, 33, and 33 in the large, medium, and small groups respectively. Among the eighty-five keywords in "all groups" in Table 4, there existed large variations that the same keyword appeared with varied frequencies in different groups. The highest occurrences concentrated in the large group, then declined as the rank of the document pool went down (see Table 5). For example, "children" had sixty-nine occurrences in the large group but decreased to twenty-six and nine respectively in the medium and small groups. While the numbers of unique keywords in the three groups did not differ significantly (p [is less than] 0.05), the relative occurrences (4.2, 2.6, 2.5 respectively) show that more records in the large group had this keyword. This similar phenomenon happened throughout most other co-occurring keywords in either all three groups or any of the two groups together. Very few keywords that occurred in the small group outnumbered the occurrences in the medium or large group--i.e., although keywords co-occurred in different groups, they did not appear at the same frequency. Keywords co-occurring in only two groups were mostly those with lower frequencies. Figure 4 depicts the number of unique keywords having occurrences one through more than nineteen. Most unique keywords in the large group occurred more frequently but much less frequently (only one, two, or three times) in the small group.

Table 4. NUMBER OF UNIQUE KEYWORDS THAT OCCURRED OR CO-OCCURRED IN DIFFERENT GROUPS

               Large Group   Medium Group   Small    All Groups
                                            Groups

Large Group         25            46           7
Medium Group        46            33          28
Small Group          7            28          33
All Groups          85            85          85          85
Total              163           192         153

TABLE 5. PORTION OF THE FREQUENCY AND PERCENTAGE OF THE KEYWORDS THAT CO-OCCURRED

Keywords Occurring           Large Group   Medium Group
in All Three Groups          Freq.    %    Freq.    %

Children/Infants/             69     4.2   26      2.6
  Pediatric patients
Susceptibility                60     3.7    3      0.3
Pneumococci                   47     2.9   21      2.1
Infection/infections          44     2.7   13      1.3
Day-care                      42     2.6   22      2.2
United States                 37     2.3    6      0.6
Haemophilus-influenza         32     2.0   34      3.4
Therapy/therapeutic           30     1.8    1      0.1
Penicillin resistance         28     1.7   19      1.9
Penicillin-binding protein    24     1.5   22      2.2
Penicillin                    22     1.3    6      0.6
Strains                       21     1.3    2      0.2
Disease                       18     1.1    6      0.6
Epidemiology                  17     1.0   11      1.1
Failure                       17     1.0    9      0.9
Otitis-media                  16     1.0    9      0.9
Vaccine/conjugate             16     1.0    2      0.2
  vaccine

Keywords Occurring           Small Group
in All Three Groups          Freq.    %

Children/Infants/             9      2.5
  Pediatric patients
Susceptibility                7      1.9
Pneumococci                   4      1.1
Infection/infections          7      1.9
Day-care                      5      1.3
United States                 7      1.9
Haemophilus-influenza         3      0.8
Therapy/therapeutic           7      1.9
Penicillin resistance         4      1.1
Penicillin-binding protein    5      1.3
Penicillin                    1      0.3
Strains                       1      0.3
Disease                       3      0.8
Epidemiology                  2      0.5
Failure                       4      1.1
Otitis-media                  1      0.3
Vaccine/conjugate             2      0.5
  vaccine

THE KEYWORD DENSITY

To compute the keyword density per rank, the frequency distribution of keyword occurrences was plotted for each of the three groups after the intellectual base keywords had been excluded. Figure 6 reveals a sharp turn at four, which was then used as a dividing point between the marginal and specialty keywords in the sample. In other words, keywords occurring three or fewer times in the sample were assumed to be marginal in the subject under study, and those with four or more times to be the specialties. Applying Formula [1] in the Data Analysis section, the keyword density was calculated according to the data in Table 6. When calculating the keyword density, ranks that had no keyword occurrences were treated as missing cases and ignored because only the actual number of frequency ranks reflected the keyword density. Thus the number of ranks for specialty, keywords in the large group would be 42 minus 3 (intellectual base ranks) minus 3 (marginal ranks) minus 5 (missing cases) equal 31, and so forth for the other two groups. Results in Table 7 show that the density for marginal keywords is approximately ten times greater than those of specialty keywords in all three groups. Further studies are needed to explore whether this is only a coincidence for this particular data set or a phenomenon existing across disciplines.

[Figure 6 ILLUSTRATION OMITTED]

Table 6. FREQUENCY DISTRIBUTION OF KEYWORD OCCURRENCES IN THREE GROUPS EXCLUDING THE THREE INTELLECTUAL BASE KEYWORDS

                        Number of Unique
                      Keywords ([t.sub.i])

        Keyword       Large   Medium   Small
No.     Occurrences   Group   Group    Group

 1         1           33      72       83
 2         2           26      30       24
 3         3           18      26       15
 4         4           10       9        9
 5         5            8       5        7
 6         6            9       8        2
 7         7            1       4        8
 8         8            6       5        1
 9         9            5       6        1
10        10            5
11        11            2       4        1
12        12            2       2        1
13        13            5       2
14        14            4       2
15        15            1       1
16        16            4       3
17        17            3                1
18        18            1       2
19        19                    3
20        20            1       1
21        21            1       2
22        24            1
23        28            1
24        30            1       1
25        32            2
26        34                    1
27        36            1
28        37            1
29        40                    1
30        42                    1
31        43            1
32        44            1
33        47            1
34        48            1
35        51            1
36        52            1
37        59            1
38        60            1
39        69            1
40        84            1
41        85            1
42       129            1

Total                 163     192      153

Table 7. KEYWORD DENSITY IN GROUPS

Keyword       Intellectual Base   Specialty
Density (D)   Keywords (i)        Keywords (s)

Large
Group (1)     D(li)=3/3=1         D(ls)=83/31=2.68

Medium
Group (m)     D(mi)=3/3=l         D(ms)=61/19=3.21

Small
Group (s)     D(si)=3/3=1         D(ss)=28/6=4.67

Keyword       Marginal
Density (D)   Keywords (m)

Large
Group (1)     D(lm)=77/3=25.67

Medium
Group (m)     D(mm)=128/3=42.67

Small
Group (s)     D(sm)=122/3=40.67

A further examination was made for keywords in the specialty and marginal groups. Several patterns emerged in the specialty keywords (see Tables 8, 9, and 10):

* Keywords co-occurring in two or three groups tended to be more generic or disciplinarily generic than non-co-occurring ones. Examples included children, day-care, failure, infections, prevalence, United States, genes.

* There were more microbial names and related infections in the keywords co-occurring than in the ones not co-occurring. Examples included pneumococci, enterococcus/enterococci, Escherichia-coli, Klebsiella-pneumonia, Neisseria-gonorrhoea, haemophilus-influenza, streptococcus-pneumonicoccal meningitis, Branhamella-catarrhalis.

* There was a clear tendency in the keywords both co-occurring and non-co-occurring (the latter happened in the first two groups only) that antibiotic resistance in pneumonia was investigated from perspectives of genetics (binding protein gene, penicillin-binding proteins, multiresistant clone), microbiology (invitro activities), and immunology (pneumococcal polysaccharide). However, this tendency in co-occurring keywords seemed to be more toward pharmaceutical aspects in relation to the microbes and infections they caused (spectrum betalactam, chloramphenicol therapy, third-generation cephalosporins), and more pathologically oriented in non-co-occurring keywords (serotype distribution, strains, antimicrobial susceptibility, plasmids).

* The keyword density in double digits were generally more specific than those in single digits, though there did exist a few general ones (see Table 10).

Table 8. SPECIALTY KEYWORDS THAT CO-OCCURRED IN TWO OR THREE GROUPS

                              Large Group   Medium Group

No.   Keywords                Freq.    %    Freq.    %

 1    Children/Infants/        69     4.2    26     2.6
      Pediatric patients
 2    Pneumococci              47     2.9    21     2.1
 3    Infection/infections     44     2.7    13     1.3
 4    Day-care/Day-care        42     2.6    22     2.2
      centers
 5    United States            37     2.3     6     0.6
 6    Penicillin resistance    28     1.7    19     1.9
 7    Penicillin-binding       24     1.5    22     2.2
      proteins
 8    Failure                  17     1.0     9     0.9
 9    Gene/genes               14     0.9    15     1.5
10    Pneumococcal             14     0.9     7     0.7
      polysaccharide
11    Prevalence               13     0.8    11     1.1
12    Enterococcus/
      enterococci               6     0.4    16     1.6
13    Escherichia-coli          5     0.3    16     1.6
14    Spectrum beta-lactam      5     0.3    18     1.8
15    Klebsiella-pneumoni       4     0.2     9     0.9
16    Neisseria-gonorrhoea      4     0.2     4     0.4
17    Meningitis               52     3.2    16     1.6
18    Chloramphenicol          36     2.5     8     0.8
      therapy
19    Haemophilus-influenza    32     2.0    34     3.4
20    Penicillin               22     1.3     6     0.6
21    Disease                  18     1.1     6     0.6
22    Epidemiology             17     1.0    11     1.1
23    Binding protein gene     16     1.0    14     1.4
24    Otitis-media             16     1.0     9     0.9
25    Streptococcus-           15     0.9    14     1.4
      pneumonicoccal
      meningitis
26    Bacterial-meningitis     14     0.9    11     1.1
27    Bacteria                 13     0.8     6     0.6
28    Beta-lactam              13     0.8     8     0.8
      antibiotics
29    Branhamella-             12     0.7     7     0.7
      catarrhalis
30    Multiresistant clone     12     0.7     8     0.8
31    Antibiotics              11     0.7     9     0.9
32    Influenzae type-b        11     0.7    11     1.1
33    Invitro activities       10     0.6     5     0.5
34    Carriage                  9     0.6     4     0.4
35    Diagnose                  9     0.6     4     0.4
36    Resistance                9     0.6     6     0.6
37    Erythromycin              8     0.5     4     0.4
38    Staphylococcus-aureu      8     0.5    11     1.1
39    Influenzae                4     0.2     5     0.5
40    Tuberculosis              4     0.2     6     0.6
41    Susceptibility           60     3.7
42    Therapy/Therapeutic      30     1.8
43    Emergence                 8     0.5
44    Protective efficacy       5     0.3
45    3rd-generation                          6     0.6
      cephalosporins
46    Enterobacter/                           7     0.7
      Enterobacteriaceae
47    Respiratory-tract                       4     0.4
      infection

                              Small Group

No.   Keywords                Freq.    %

 1    Children/Infants/         9     2.4
      Pediatric patients
 2    Pneumococci               4     1.1
 3    Infection/infections      7     1.9
 4    Day-care/Day-care         5     1.3
      centers
 5    United States             7     1.9
 6    Penicillin resistance     4     1.1
 7    Penicillin-binding        5     1.3
      proteins
 8    Failure                   4     1.1
 9    Gene/genes                4     1.1
10    Pneumococcal              7     1.9
      polysaccharide
11    Prevalence                5     1.3
12    Enterococcus/
      enterococci               4     1.1
13    Escherichia-coli          7     1.9
14    Spectrum beta-lactam      5     1.3
15    Klebsiella-pneumoni       6     1.6
16    Neisseria-gonorrhoea      6     1.6
17    Meningitis
18    Chloramphenicol
      therapy
19    Haemophilus-influenza
20    Penicillin
21    Disease
22    Epidemiology
23    Binding protein gene
24    Otitis-media
25    Streptococcus-
      pneumonicoccal
      meningitis
26    Bacterial-meningitis
27    Bacteria
28    Beta-lactam
      antibiotics
29    Branhamella-
      catarrhalis
30    Multiresistant clone
31    Antibiotics
32    Influenzae type-b
33    Invitro activities
34    Carriage
35    Diagnose
36    Resistance
37    Erythromycin
38    Staphylococcus-aureu
39    Influenzae
40    Tuberculosis
41    Susceptibility            7     1.9
42    Therapy/Therapeutic       7     1.9
43    Emergence                 4     1.1
44    Protective efficacy       4     1.1
45    3rd-generation            8     2.2
      cephalosporins
46    Enterobacter/             5     1.3
      Enterobacteriaceae
47    Respiratory-tract         4     1.1
      infection

Table 9. SPECIALTY KEYWORDS OCCURRING IN A SINGLE GROUP

             Keywords Unique in the
No.               Large Group                Freq.    %

 1    Serotype distribution                   48     2.9
 2    Spain                                   32     2.0
 3    Strains                                 21     1.3
 4    New-Guinea/Papua-New-Guinea             17     1.0
 5    Vaccine/Conjugate vaccine               16     1.0
 6    Pneumococcal meningitis                 14     0.9
 7    Systemic infections                     13     0.8
 8    Penicillin-resistant pneumoniae         13     0.8
 9    Resistant pneumococcus pneumoniae       10     0.6
10    Upper respiratory-tract                 10     0.6
11    Community-acquired pnuemoniae           10     0.6
12    Immune-deficiency syndrome               9     0.6
13    Antibody                                 9     0.6
14    Vancomycin                               8     0.5
15    Horizontal transfer                      8     0.5
16    Antimicrobial susceptibility             8     0.5
17    Hungary                                  7     0.4
18    Iceland                                  6     0.4
19    Invasive disease                         6     0.4
20    Patterns                                 6     0.4
21    Pneumococcal infections                  6     0.4
22    Acquired immuno deficiency syndrome      6     0.4
23    Bacterial pneumonia                      6     0.4
24    Cerebrospinal-fluid                      6     0.4
25    Co-trimoxazole                           6     0.4
26    Requiring hospitalization                5     0.3
27    Sensitivity                              5     0.3
28    Septic arthritis                         5     0.3
29    Human-Immuno deficiency Virus (HIV)      5     0.3
30    Capsular polysaccharide                  5     0.3
31    Molecular epidemiology                   4     0.2
32    Invasive pneumococcal infections         4     0.2
33    Anemia                                   4     0.2
34    Binding proteins                         4     0.2
35    Capsular types                           4     0.2
36    Ciprofloxacin                            4     0.2
37    UK                                      30     3
38    Sulbactam                               19     1.9
39    Resistant staphylococcuci               18     1.8
40    Nucleotide-sequences                    13     1.3
41    Sri-Lanka                               12     1.2
42    Cephalosporins                           9     0.9
43    Pneumococcal serotype                    9     0.9
44    Tetracycline                             8     0.8
45    Transpeptidase                           8     0.8
46    Mechanism                                6     0.6
47    Catarrhalis beta-lactamase               5     0.5
48    Pneumococcal vaccine                     5     0.5
49    Postsplenectomy sepsis                   5     0.5
50    Ampicillin                               4     0.4
51    Gram-negative bacilli                    4     0.4
52    Plasmid/plasmids                         4     0.4
53    Mechanically ventilated patients         7     1.9
54    Patients/critically ill patients         7     1.9
55    Intensive-care unit (AIDS)               5     1.3
56    Nosocomial infection                     5     1.3
57    Transferable resistance                  4     1.1

Table 10. MARGINAL KEYWORDS THAT CO-OCCURRED IN EITHER ALL THREE OR TWO OF THE THREE GROUPS

                                    Large Group   Medium Group

Keywords                            Freq.    %    Freq.    %

Pseudomonas-aeruginosa                3     0.2     3     0.3
Management                            3     0.2     3     0.3
Etiology                              3     0.2     1     0.1
Isolate/clinical isolate              2     0.1     2     0.2
Coagulase-negatives                   2     0.1     2     0.2
Aminoglycoside resistance             2     0.1     1     0.1
Legionnaires-disease                  2     0.1     1     0.1
Microdilution system                  2     0.1     1     0.1
Blood cultures                        2     0.1     2     0.2
Trimethoprim-sulfame                  1     0.1     2     0.2
Methicillin-resistant                 1     0.1     2     0.2
Refractory periodont                  1     0.1     1     0.1
Outer-membrane permeability           1     0.1     3     0.3
Outbreak                              1     0.1     3     0.3
Nosocomial outbreak                   1     0.1     3     0.3
Colonization                          1     0.1     3     0.3
2x                                    2     0.1     2     0.2
Anti-inflammatory agent               3     0.2     1     0.1
Antibiotic-therapy                    1     0.1     1     0.1
Aspiration                            1     0.1     1     0.1
Broth                                 1     0.1     1     0.1
Cefamandole                           3     0.2     1     0.1
Ceftriaxone                           3     0.2     1     0.1
Clarithromycin                        1     0.1     2     0.2
Clindamycin                           1     0.1     1     0.1
Clones                                2     0.1     2     0.2
Common organization                   2     0.1     1     0.1
D-alanine ligase                      2     0.1     3     0.3
Directions                            1     0.1     1     0.1
Group-a                               1     0.1     1     0.1
High-level resistance                 2     0.1     3     0.3
Invasive pneumococcal infections      1     0.1     1     0.1
Nasopharyngeal carriage               3     0.2     2     0.2
Neisseria-meningitis                  1     0.1     2     0.2
Pathogen                              1     0.1     1     0.1
Populations                           3     0.2     2     0.2
Quinolones                            1     0.1     1     0.1
South-Africa                          2     0.1     1     0.1
Spread                                3     0.2     1     0.1
Streptococcus-pneumoniae strains      2     0.1     1     0.1
Structural-changes                    1     0.1     1     0.1
Ampicillin                            3     0.2
Antimicrobial agents                  3     0.2
Bacterium legionella                  2     0.1
Catarrhalis beta-lactamase            3     0.2
Cephalosporins                        2     0.1
Dirithromycin                         1     0.1
Mechanism                             2     0.1
Norfloxacin                           1     0.1
Nucleotide-sequences                  2     0.1
Plasmid/plasmids                      2     0.1
Pneumococcal vaccine                  1     0.1
Spectrum                              1     0.1
Affairs-medical-center                              2     0.2
Anemia                                              1     0.1
Antibody                                            3     0.3
Aztreonam                                           1     0.1
Broad-spectrum cepha                                1     0.1
Calcoaceticus var anitratus                         2     0.2
Capsular polysaccharide                             3     0.3
Ceftazidime resistance                              3     0.3
Cerebrospinal-fluid                                 3     0.3
Ciprofloxacin                                       3     0.3
Classification                                      2     0.2
Community-acquired pnuemoniae                       2     0.2
Digestive-tract                                     1     0.1
DNA                                                 3     0.3
Enzymatic resistance                                3     0.3
Horizontal transfer                                 1     0.1
Identification                                      1     0.1
Imipenem-cilastatin                                 3     0.3
India                                               1     0.1
Nursing-home patient                                3     0.3
Patterns                                            1     0.1
Penicillin-resistant pneumoniae                     3     0.3
Pneumococcal meningitis                             3     0.3
Resistant pneumococcus pneumoniae                   3     0.3
Salmonella-typhi                                    1     0.1
Selective decontamination                           2     0.2
Staphylococcus-aureu                                3     0.3
Steady-state treatment                              2     0.2
Strains                                             2     0.2
Substitution                                        1     0.1
Systemic infections                                 2     0.2
Third-world countries                               1     0.1
Transposition                                       1     0.1
Upper respiratory-tract                             2     0.2
Vancomycin                                          1     0.1

                                    Small Group

Keywords                            Freq.    %

Pseudomonas-aeruginosa                2     0.5
Management                            1     0.3
Etiology                              1     0.3
Isolate/clinical isolate              1     0.3
Coagulase-negatives                   1     0.3
Aminoglycoside resistance             2     0.6
Legionnaires-disease                  1     0.3
Microdilution system                  1     0.3
Blood cultures                        1     0.3
Trimethoprim-sulfame                  1     0.3
Methicillin-resistant                 1     0.3
Refractory periodont                  1     0.3
Outer-membrane permeability           1     0.3
Outbreak                              1     0.3
Nosocomial outbreak                   2     0.5
Colonization                          3     0.8
2x
Anti-inflammatory agent
Antibiotic-therapy
Aspiration
Broth
Cefamandole
Ceftriaxone
Clarithromycin
Clindamycin
Clones
Common organization
D-alanine ligase
Directions
Group-a
High-level resistance
Invasive pneumococcal infections
Nasopharyngeal carriage
Neisseria-meningitis
Pathogen
Populations
Quinolones
South-Africa
Spread
Streptococcus-pneumoniae strains
Structural-changes
Ampicillin                            1     0.3
Antimicrobial agents                  1     0.3
Bacterium legionella                  1     0.3
Catarrhalis beta-lactamase            1     0.3
Cephalosporins                        3     0.8
Dirithromycin                         1     0.3
Mechanism                             2     0.5
Norfloxacin                           1     0.3
Nucleotide-sequences                  2     0.5
Plasmid/plasmids                      2     0.5
Pneumococcal vaccine                  1     0.3
Spectrum                              1     0.3
Affairs-medical-center                1     0.3
Anemia                                1     0.3
Antibody                              1     0.3
Aztreonam                             1     0.3
Broad-spectrum cepha                  1     0.3
Calcoaceticus var anitratus           1     0.3
Capsular polysaccharide               1     0.3
Ceftazidime resistance                1     0.3
Cerebrospinal-fluid                   2     0.5
Ciprofloxacin                         1     0.3
Classification                        1     0.3
Community-acquired pnuemoniae         2     0.5
Digestive-tract                       3     0.8
DNA                                   3     0.8
Enzymatic resistance                  2     0.5
Horizontal transfer                   2     0.5
Identification                        1     0.3
Imipenem-cilastatin                   3     0.8
India                                 1     0.3
Nursing-home patient                  1     0.3
Patterns                              1     0.3
Penicillin-resistant pneumoniae       1     0.3
Pneumococcal meningitis               3     0.8
Resistant pneumococcus pneumoniae     1     0.3
Salmonella-typhi                      1     0.3
Selective decontamination             3     0.8
Staphylococcus-aureu                  2     0.5
Steady-state treatment                1     0.3
Strains                               1     0.3
Substitution                          1     0.3
Systemic infections                   1     0.3
Third-world countries                 2     0.5
Transposition                         1     0.3
Upper respiratory-tract               3     0.8
Vancomycin                            1     0.3

CONCLUSION

Knowledge discovery in bibliographic databases is distinctive compared to KD in full-text document and numerical databases. One challenge is transforming semi-structured textual data into the types and structures suitable for calculations and modeling. In the case of subject keywords, all the idiosyncrasies existing in natural language, including suffixes, different spellings for the same word, and synonyms, need to be normalized before analysis.

Similar work on this type of term normalization has been done in automatic indexing, such as stem stripping (Paice, 1990; Porter, 1980). Harman and Candela (1990) argue that term normalization such as stem stripping is not worth the effort for large full-text databases because this operation has little impact on other methods (e.g., frequency counts) of indexing. While this may be true in indexing full-text documents, preprocessing of this kind is a necessity in discovering knowledge from bibliographic databases. The reason is obvious: semantic analysis of subject keywords needs to have accurate data to draw reliable and valid conclusions. The unnormalized keyword data set can present false patterns or trends in keywords. Although term normalization is a time-consuming operation, it can be improved by making use of the prior research and database technology mentioned earlier. In this study, as the initial text code base took shape, coding became easier and quicker as more and more text codes were established. It was found that semantic coding, while resembling vocabulary control, is different from vocabulary control in indexing. Semantic coding groups semantically same and/or similar keywords together by using simple codes that can be easily constructed. Using these codes, original terms can be preserved with semantic value-added processing, thus there is no need for using totally different "controlled" terms to substitute the keywords used in the publications. It quantifies the information analysis process and turns the jobs requiring expert knowledge into relatively simple tasks. This method is particularly suitable for specialized and interdisciplinary subject fields.

Presentation of the knowledge discovered is an important part of the KDD process. Visualizing the patterns, trends, and associations in a subject field can be very challenging because of the size of the screen and the number of text values that one data field can contain. This study of semantic patterns in keywords was by no means a large one in scale, but the total number of keywords made it difficult to draw any legible charts for the whole data set. An inclusion of even one group of keywords would clutter the chart badly and cause the keywords on the chart to be unrecognizable. Substituting long keywords with shorter and mnemonic text codes normalized the inconsistencies in keywords as well as leaving more room for visual presentation of the knowledge discovered.

The semantic patterns discovered in this data set suggest that different keyword density regions may be used as a controlling mechanism for better targeted searching. Traditionally, query expansion is one of the main techniques used to improve retrieval performance (Sparck Jones & Jackson, 1970; Salton, Fox, & Voorhees, 1983; Salton & Buckley, 1990; Harman, 1992). Query expansion allows searchers to browse the indexing term list or give relevance feedback to searchers through frequency ranking or term weighting. While performance was reported to have improved to a high percentage in small testing collections, it is still unproven that these techniques would achieve the same performance in large collections in the real world (Korfhage, 1997). Keyword density may provide a new solution to this uncertainty because it is computed on the basis of a collection of keywords extracted from bibliographically coupled source documents. By implementing keyword density analysis into an algorithm, it is possible that a simple search query to the database (s) would generate a group of keywords stratified by their density regions. Information searchers can then select keywords from different density regions according to their own definition of relevance.

The semantic patterns found in non-co-occurring and co-occurring keywords suggest that it is necessary and possible to design new search tools that will deliver "analyzed" search results to users. In retrieving information from terabyte databases, the most challenging task in information retrieval is probably how to find most relevant information, in a manageable amount, in the easiest way. Conventional information systems have applied various sophisticated methods to accomplish this task but were limited by their design which requires equally sophisticated search techniques to find the information and leaves the information filtration to users themselves. The development of science and the growth of scientific literature has made filtering relevant information more difficult than ever in highly interdisciplinary scientific research areas. The semantic pattern analysis of the keywords from bibliographical coupling shows a possibility that simple semantic processing to natural language (keywords extracted from citations in this case) may be programmed and serve as a tool for providing "analyzed" search results to users.

The results in this study are only preliminary. It is unknown whether the semantic patterns identified in this data set are a coincidence or a common phenomenon across subject fields. Further studies are needed to discover whether the subject category of keywords is related to the density region and whether the stratified keyword distribution and density can contribute to customizing the selection of a targeted group of documents and post-search analysis.

[Figure 5 ILLUSTRATION OMITTED]

REFERENCES

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ADDITIONAL REFERENCE

Small, H.; Sweeney, E.; & Greenlee, E. (1985). Clustering the Science Citation Index using co-citations: II. Mapping science. Scientometrics, 8(5/6), 321-340.

APPENDIX

EXAMPLES OF KEYWORDS AND THEIR SEMANTIC CODES IN THE SAMPLE

Keyword            Code       Keyword              Code

2x                 2x         HUMAN-IMMUNO-        hiv
                               DEFICIENCY VIRUS

ANTI-INFLAMM-      agnt       HUNGARY              hungary
 ATORY AGENT

AID                Saids      IMMUNE-DEFICIENCY    Eids
                               SYNDROM

ANTIMICROBIAL      sus-am     INVASIVE PNEUMO-     Sinf-pnu
 SUSCEPTIBILITY                COCCAL INFECTION

ASPIRATION         aspirat    PNEUMOCOCCAL         inf-pnu
                               INFECTIONS

BARCELONA          barc       INVASIVE DISEASE     invasiv

BINDING PROTEINS   bp         MENINGITIS/          meningi
                               MENINGEAL

BINDING PROTEIN    bpg        MOLECULAR            epi-mol
 GENE                          EPIDEMIOLOGY

BROTH              broth      NEW-GUINEA/          ng
                               PAPUA-NEW

CAPSULAR TYPES     capt       COMMON ORGAN-        org
                               IZATION
CARRIAGE           carrig     PATHOGEN             pathoge

NASOPHARYNGEAL     carr-n     BACTERIAL            pnu-b
 CARRIGE                       PNEUMONIA

CEFAMANDOLE        cefam      QUINOLONES           quinolo

CEFTRIAXONE        ceftri     HIGH-LEVEL           res-hi
                               RESISTANCE

CHLORAMPHEN        ther-chl   SOUTH-AFRICA         sa
 -ICOL THERAPY

CLARITHROMYCIN     clarith    SENSITIVITY          sensiti

CLINDAMYCIN        clindam    POSTSPLE- SEPSIS     sepsi-p
                               NECTOMY

CLONES             clone      SPREAD               spread

MULTIRESISTANT     clone-m    STREPTOCOCCUS        stra-s
 CLONE                         -PNEUMONIAE
                               STRAINS

DIRECTIONS         direct     SOUTH-AFRICAN        stra-sa
                               STRAIN

D-ALANINE LIGASE   ligase     STRUCTURAL-          struct
                               CHANGES

ERYTHROMYCIN       erythr     TETRACYCLINE         tetracy

GROUP-A            grp-a      ANTIBIOTIC-THERAPY   ther-a

Jian Qin, School of Information Studies, Syracuse University, 4-206 Center for Science and Technology, Syracuse, NY 13244

JIAN QIN is Assistant Professor at the School of Information Studies at Syracuse University in Syracuse, New York. She was the recipient of the OCLC LIS Research Grant in 1997 and the ISI Citation Research Grant in 1997. Ms. Qin is the author of over twenty journal articles, technical reports, and conference papers dealing with scientific communication, metadata, keyword semantic pattern analysis, and bibliometrics. More recently she co-edited a topical issue on Web research and information retrieval for Information Processing and Management.3