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SGML Extended Facilities

Charles F. Goldfarb

HyTime 2 (ISO/IEC 10744:1997)

Two standards in one document
- SGML Extended Facilities
- Enhanced HyTime architecture
Extended Facilities will become part of ISO 8879: SGML.

SGML Extended Facilities Overview

For all SGML, not just HyTime
Will move to revised SGML standard
Definition requirements for
- Architectural Forms (AFDR)
- Groves and Property Sets (PSDR)
- Formal System Identifiers (FSIDR)
- Lexical Types (LTDR)
"General Architecture"
Modular conformance: use any or all

Architectural Form Definition Requirements (AFDR)

Define "enabling architectures" for SGML documents
Element type, attribute, and notation forms
Permits common processing tools across multiple document types
Documents are "derived" from architectures
Multiple derivation levels and/or bases

Key AFDR Concepts

Client document is "derived" from one or more "base" architectures (meta-DTDs)
Client identifies its base architectures via "architecture support declarations"
Any DTD can be a meta-DTD (even a derived DTD)
An SGML parser can recognize "architectural instances" (as well as normal document instance)

Architecture Benefits

Proven technique since 1990
Provides OOPS-like inheritance of attributes, content models
Manages multiple name spaces without conflict
No new syntax: use with any DTD (e.g., HTML)
Transparent to normal SGML parsing
Free implementation in SP

Property Set Definition Requirements (PSDR)

Classes and properties recognized by a parsing process
- SGML is one such process
- HyTime datatok is another
SGML classes include elements, attributes, data characters
Properties of SGML elements include element type, markup, etc.
Property set definition document for any notation

Graph Representation Of property ValuEs (GROVE)

Structure created by a parsing process
- Graph nodes are instances of classes
- Graph arcs are properties of nodes
"Grove plan" determines which classes and properties are included
Grove contains multiple connected trees
Groves linked to form hypergroves
Common object model for any notation

General Architecture

Extensions to SGML semantics
Immediate reference typing
Attribute inheritance with default value lists for implied attributes
- DVL: Inheritance from ancestors
- AFDR: Inheritance from base classes
Modular conformance: use any or all

Formal System Identifier Definition Requirements (FSIDR)

Coexists with informal system IDs
FSI definition document describes all system storage facilities
Multiple storage managers permitted
- Local: osfile, osfd
- Portable: url, neutral, mimetype
- Global: literal, ThisOne
- Container: sbento, tar, mime

Lexical Type Definition Requirements (LTDR)

Lexical types for attribute values, data content, pattern matching, addressing
Single definition mechanism for all uses
Use any modeling notation: Posix regular expressions, HyLex, et. al.
LTDR + AFDR + SGML provide generalized extensible schema facility
- Transparent to parsers
- Fully standardized; no ad hoc code
- Doesn't confound lexical and structural

HyTime Architecture Enhancements

Facilities aligned with DSSSL
- SDQL with HyTime addressing
- Core expression language
- Common SGML grove
Location addressing: grove-based (transparently), extensible
Hyperlinking: more link forms
Scheduling: fcsloc, calibrated schedules

Foundation for Future of SGML and XML

Data modeling and precise document type definition (LTDR, AFDR)
Network-awareness with no change to document instances (FSIDR)
Common object model for all notations (PSDR, groves)
Name spaces (AFDR)
Inherited attribute values and content models (AFDR, GA)
Rich linktyping and locating (HyTime)

For Further Information ...

Visit the HyTime Users' Group at www.hytime.org