Essential
XML; Beyond Markup
ISBN:
0-201-70914-7
Pages: 352
Publisher: Addison Wesley
Authors: Don Box, AAron Sonnard, and John Lam
Intended Audience:
Essential
XML is intended for the software
practitioner. The book is designed to reveal
the "truth" about XML. That is,
the book was written to help developers sort out
when XML makes sense, and likewise when it
doesn't. To quote the authors in the
preface, "The trade press has anointed XML as
the universal duct tape for all software
integration problems...whether it makes sense or
not."
Summary:
Essential
XML is written from the prospective of what the
authors consider to be the most pivotal
specification, the XML Information Set (Infoset).
They believe the Infoset to be the most important
because it describes exactly what an XML document
is in syntax-free terms. According to the
authors, the most interesting XML technologies are
written in terms of the Infoset. The authors
therefore begin this book with a look at XML
beyond the syntax of the markup, from the Infoset
point of view.
The
second chapter of Essential XML focuses on the
programming interfaces to XML. Here the
authors provide an overview to SAX2 (Simple API
for XML) and DOM2 ( Document Object Model Level
2). The authors describe the similarities
and differences and provide concrete examples of
the use of SAX2 and DOM2.
The
third chapter focuses on the suite of XML
specifications that enable navigating XML
structures and enable addressing. Here
authors focus on XPath, XPointer, XInclude, and
XBase. This chapter is filled with diagrams
illustrating the navigation models and a host of
examples. A great deal of time is spent on
XPath expressions and functions.
Chapter
4 focuses on XML Schemas. According to the
authors, "XML documents exchanged between
software agents rarely consist of arbitrary,
unconstrained markup." Schemas enable
both software and humans to know what content to
expect in XML documents that are exchanged.
These authors do not consider DTDs at all, stating
that "XML Schema subsumes the functionality
of ... DTDs." Again the
chapter is filled with examples. Most useful
is the table of simple type facets that helps
programmers understand how the data types may be constrained.
Chapter
5 focuses on one of the most useful of the XML
core family of standards, XSLT for performing
transformations. These authors consider XSLT
to be a "programming language" and
compare it to other programming languages such as
Perl, Active Server Pages, and Java Server
Pages. In addition to providing examples
where XSLT uses literal result elements as the
stylesheet, this chapter provides the technique
for developing stylesheets that are a series of
one or more template rules that can be invoked
with either symbolic names or template rules based
on pattern matching.
The
final chapter of Essential XML is most
interesting. It provides a look at the state
of component software today (without XML) and then
examines how XML may (or may not) change the way
component software is written in the future.
According to the authors, "despite the hype
surrounding XML... simply adopting XML ans an
integration technology is fairly meaningless." The emerging SOAP
specification (also authored by Don Box) is highlighted
in this chapter to show how XML can be useful to
develop a framework for layering extensions into a
message format. The authors conclude that
the nature of XML schemas "force one to
reevaluate exactly what an object is and whether
this term is even meaningful..."
This
book is a departure from other developer texts
that compartmentalize XML and its family of
specifications. It is written from the
prospective of the InfoSet. It relates other
specifications and technologies to XML in a
seamless fashion and will prove truly useful not
only to experienced developers, but to those
developing new Web specifications as well.
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