Page 90 - Intelligent Communication Systems

CHAPTER 7 / NEWLY DEVELOPED TELECOMMUNICATION SERVICES 73
7.8.9 CALS Standards

The CALS standards that have been standardized by ISO are SGML, COM, IGES,
and STEP. Some of their important specifications are described next.

7.8.9.1 Standard Generalized Markup Language (SGML)
Standard Generalized Markup Language (SGML) is the standard for describing
text. Generally speaking, the markup is used to edit a document. It specifies the
beginning and end of the text, the writing styles, and the fonts. The markup spec-
ification depends on the manufacturer and therefore may be incompatible with
another specification. For example, it is possible to exchange the textual data of a
document created by MS-DOS. However, it is difficult to exchange gothic char-
acters and tables written by means of MS-DOS. With the introduction of SGML,
it became possible to exchange a document that includes gothic characters and
tables. One of the major functions of SGML is to create a document using the
skeleton of the document. SGML provides a document-type definition (DTD)
facility by which a document can be constructed in structural form. For example,
if a document consists of a title, an abstract, chapters with sections, and a conclu-
sion, SGML functions can put the document in its structural form. This also makes
it easy to revise the document by erasing a part of it or adding a new part. It is easy
to handle the document written by SGML in a database, because the document is
structured into, say, its title, abstract, chapters and sections, and conclusions. The
document can be easily retrieved from a database by specifying merely its title.
Documents that are especially suited to SGML standards include form documents,
documents where a specific part is frequently modified, documents that are down-
loaded to different equipment, documents retrieved from a database, and docu-
ments written by two or more authors.

7.8.9.2 Computer Graphics Metafile (CGM)
The Computer Graphics Metafile (CGM) is one of the CALS standards for figures,
tables, and illustrations. Whereas SGML focuses only on the standard for a docu-
ment, CGM covers the figures and those documents where figures are included.

7.8.9.3 Initial Graphics Exchange Specification (IGES)
The Initial Graphics Exchange Specification (IGES) specifies the standard for
design table produced via CAD. IGES was initially standardized by ANSI and has
been implemented as a standard for CALS.

7.8.9.4 Standards for the Exchange of Product (STEP)
The Standards for the Exchange of Product (STEP) model data focus on the man-
ufacturing process. In the manufacturing process, not only design tables but also
revised information on the design tables, the configuration of the final product, and
sales information have to be taken into consideration. The goal of STEP is to pro-
vide the functions by which the companies around the world can easily and freely