Advantages of using SGML.
This article examines the background leading to the development of SGML, advantages of SGML, and difficulties encountered when first using SGML.
With computers being used for text processing, problems arise in handling the text. For example, formats used by different manufacturers are incompatible. Although documents are stored on computers, documents generally have to be converted to another text processing type to be used on a different computer. This conversion entails much time and effort.
Therefore, within the last decade, there has been a focus on document portability. It was recognized that, to access documents on different computers, there had to be standardization. In October 1986, the International Organization for Standardization (ISO) designated a standard for document representation - SGML (International Standard 8879). This standard views documents as files composed of text and structure:
Structure ("tags") (ASCII)
SGML documents are ASCII files. ASCII files can contain uppercase and lowercase letters, numbers, and standard punctuation marks, and each character is assigned a number from 1 to 128. Therefore, SGML documents can be easily exchanged among most computers.
Since its adoption as an ISO standard, many industries are committing to SGML; for example, government agencies, aerospace, computers, telecommunications, and publishing.
Advantages of SGML
Following are just a few of the many advantages of SGML.
Using Special Tag Elements. By using special tag elements within an SGML file, text display can be altered either by the user or by front-end programs to control the text that can be printed or displayed.
Displaying system-specific information. At Unisys Corporation, we use an SGML environment developed within Unisys called Open System for Documentation Engineering (OSDE). Using the capabilities of SGML, we can tag our documentation to indicate platform-specific information using Multiple Variations Methodology (MVM). This is an optional element that we can add to our SGML documents. MVM tags enable writers to designate or tag blocks of text as specific to a hardware or software platform, a user interface, compiler level, or any other difference. One type of MVM tag that we use is the heading checkbox. An example is shown in Figure 1, where:
* OS 2200 denotes information specific to Unisys OS 2200 systems;
* Monitor denotes information specific to monitoring an Open/OLTP system;
* TD-Windows denotes information specific to Transactional Desktop for Windows.
The heading checkboxes shown in this example indicate that all text below the heading contains information about the system checked in the heading checkbox, OS 2200. However, in Figure 2, the lack of heading checkboxes at the top of a page from the same document indicates that the information on that page applies to all systems.
In addition to heading checkboxes, we also use margin brackets. These bold vertical lines in the outer margin of a page indicate information specific to a particular system. For example, if the heading checkboxes indicate that both OS 2200 and Monitor information appears on the page, margin brackets would also appear on the outer margin of the page. These margin brackets would designate what information is specific to OS 2200 and what information is specific to Monitor.
Selectively displaying text. Marking text to indicate system-specific information, as described above, offers an advantage for users in the CD-ROM environment. When viewing the CD-ROM version of the document that contains heading checkboxes shown in Figure 1, the user can hide specific types of information. By using a pull-down menu, the user can choose to hide the Monitor and TD-Windows information; this would display only OS 2200 system information.
Implementing security. SGML documents can contain information for a variety of audiences. For example, a writer can designate certain sections or paragraphs for system administrators only using special tagging similar to that described above. By using a front-end program that would check a user's user identification and password, general users are restricted from viewing the system administrator portions of an SGML document.
Reusing the Database. At Unisys, we can code our documents in SGML. From this single document database, we can produce both printed output and a CD-ROM database. OSDE tailors the format for each output medium - print or CD-ROM.
Increasing the Life Span of Documents. SGML documents have long life spans because they are device independent. For example, because the aircraft maintenance and repair manuals for Boeing Aircraft Company aircraft average several thousand pages and have a life span of at least 30 years, Boeing is writing these as SGML documents. Therefore, Boeing no longer has to convert data when it changes publishing systems (Interleaf, Inc. 1994).
Using the Internet. A subset of SGML, the HypterText Markup Language (HTML), is used for documents that are accessible on the Internet. Hypermedia documents contain links to other text, graphics, video, and sound. Many government agencies and universities are now using the Internet and the World Wide Web (WWW) to provide information about their organization and research activities.
Performing Document Translations. Documents written using SGML tags can be easily translated to other languages. This is because only the text following the SGML tags needs to be translated to another language. The SGML tags can remain unchanged.
Performing Quick Online Searches. Because SGML tags are used to denote elements or structures within documents, SGML allows for quick online searches. For example, a user can search for a specific word or phrase in a title only. Or, a user can search for the word or phrase within the document itself.
Focusing on Structure. Most "what you see is what you get" environments cause writers to focus on page layout and appearance. Therefore, the writer often overlooks the necessary structure of a document. SGML, however, is based on structure and forces writers to code consistently. For example, in some word processing environments, there is more than one command available for bold text. However, in SGML, there is only one way to code bold emphasis of text.
In addition, some environments allow writers to go from a second-level heading to a fourth-level heading. The SGML environment, on the other hand, checks for such heading inconsistencies. Therefore, an SGML document file will not validate if the validator encounters an inconsistency in heading level placement.
Difficulties Encountered When First Using SGML
With every new technology, there are difficulties encountered during its implementation. Although there are numerous advantages to using SGML, some users encounter difficulties during the early phases of SGML implementation. These include a learning curve to understand and use SGML and having to write Document Type Definitions (DTD).
Encountering a Learning Curve. Because SGML uses start and end tags, it is sometimes considered more of a programming language, rather than an environment for text processing. As with most text processing systems, it is important to provide employees with proper training in the environment in which they will be working. The same principle applies to SGML.
Developing DTDs. The advantage of SGML being specific to one's needs can also be considered a drawback, because SGML requires a DTD. A DTD defines the structure of a document. For example, a document written using the traditional format used by some companies may allow for fourth-level headings. A document written using the Information Mapping[R] method can have only three levels of headings. Therefore, each of these documents requires a different structure. Like an SGML text file, a DTD is also an ASCII file. The SGML tags within your document must correspond to those contained in the DTD you are using.
It is most helpful to design a DTD that is general enough to accommodate multiple document types that are in the same class. For example, a DTD can be general enough to contain the elements that would appear in both a manual and a proposal.
As more agencies and corporations use SGML for document interchange, its advantages are becoming evident. Therefore, as communicators, it is important to keep in mind these advantages as we communicate with the world on the Information Highway.
Interleaf, Inc. 1994. The SGML Guide. Waltham, MA.
International Organization for Standardization. 1986. ISO 8879: Information Processing - Text and Office Systems - Standard Generalized Markup Language (SGML). Geneva/New York.
van Herwijnen, Eric. 1990. Practical SGML. 2d ed. Norwell, MA: Kluwer Academic Publishers.
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|Title Annotation:||standard generalized markup language|
|Author:||Lunemann, Rhonda S.|
|Date:||May 1, 1995|
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