2. XML: Managing Document Components
XML and its parent technology, SGML (Standard Generalized Markup Language),
provide the foundation for managing not only documents but also the information
components of which the documents are composed. This is due to some notable
characteristics of XML data.
Documents vs. Files
In XML, documents can be seen independently of files. One document can
comprise many files, or one file can contain many documents. This is the
distinction described earlier in this series between the physical and
logical structure of information. XML data is primarily described by
its logical structure. In a logical structure, principal interest is placed
on what the pieces of information are and how they relate to each other,
and secondary interest is placed on the physical items that constitute
the information.
Rather than relying on file headers and other system-specific characteristics
of a file as the primary means for understanding and managing information,
XML relies on the markup in the data itself. A chapter in a document is
not a chapter because it resides in a file called chapter1.doc
but because the chapter's content is contained in the <chapter>
and </chapter> element tags.
Because elements in XML can have attributes, the components of a document
can be extensively self-descriptive. For example, in XML you can learn a lot
about the chapter without actually reading it if the chapter's markup is rich
in attributes, as in <chapter
language="English" subject="colonial economics" revision_date="19980623"
author="Joan X. Pringle" thesis_advisor="Ramona Winkelhoff">.
When the elements carry self-describing
metadata with them, systems that understand XML syntax can operate on those
elements in useful ways, just like a traditional document management system
can. But there is a major difference.
Information vs. Documents
XML markup provides metadata for all components of a document, not merely
the object that contains the document itself. This makes the pieces of
information that constitute a document just as manageable as the fields
of a record in a database. Because XML data follows syntactic rules for
well-formedness and proper containment of elements, document management
systems that can correctly read and parse XML data can apply the functions
of document management system, such as those mentioned above, to any and
all information components inside the document.
The focus on information rather than documents from XML offers some
important capabilities:
While standard document management systems do offer some measure of
information reuse through file sharing, information management systems
based on XML or SGML enable people to share pieces of common information
without storing the piece of information in multiple places.
By enabling people to focus on information components that make up documents
rather than on the documents themselves, these systems can identify and
capture useful information components that have ongoing value "buried" inside
documents whose value as documents is limited. That is, a particular
document may be useful only for a short time, but chunks of information
inside that document may be reusable and valuable for a longer period.
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Fine-granularity text-management applications
Because the information components in XML documents are identifiable,
manipulatable, and manageable, XML information management technology can
support real economies in applications such as translation of technical
manuals. (Look for an article devoted to this subject in the future.)