<Chapter Label="ch:bibutil">
<Heading>Utilities for Bibliographies</Heading>
A standard for collecting references (in particular to mathematical
texts) is &BibTeX; (<URL>https://tug.org/bibtex/</URL>).
A disadvantage of &BibTeX; is that the format of the
data is specified with the use by &LaTeX; in mind. The data format is
less suited for conversion to other document types like plain text or HTML.<P/>
In the first section we describe utilities for using data from &BibTeX;
files in &GAP;. <P/>
In the second section we introduce a new XML based data format
BibXMLext for bibliographies which seems better suited for other
tasks than using it with &LaTeX;. <P/>
Another section will describe utilities to deal with BibXMLext
data in &GAP;.
Here are functions for parsing, normalizing and printing reference lists
in &BibTeX; format. The reference describing this format is <Cite
Key="La85" Where="Appendix B"/>.
Bibliographical data in &BibTeX; files have the disadvantage that the
actual data are given in &LaTeX; syntax. This makes it difficult to use
the data for anything but for &LaTeX;, say for representations of the
data as plain text or HTML. For example: mathematical formulae are in
&LaTeX; <C>$</C> environments, non-ASCII characters can be
specified in many strange ways, and how to specify URLs for links if the
output format allows them?<P/>
Here we propose an XML data format for bibliographical data which
addresses these problems, it is called BibXMLext. In the next
section we describe some tools for
generating (an approximation to) this data format from &BibTeX; data,
and for using data given in BibXMLext format for various
purposes. <P/>
The first motivation for this development was the handling of
bibliographical data in &GAPDoc;, but the format and the tools are certainly
useful for other purposes as well.<P/>
We started from a DTD <F>bibxml.dtd</F> which is publicly available, say
from <URL>https://bibtexml.sf.net/</URL>. This is essentially a
reformulation of the definition of the &BibTeX; format, including
several of some widely used further fields. This has already the
advantage that a generic XML parser can check the validity of the
data entries, for example for missing compulsary fields in entries.
We applied the following changes and extensions to define the
DTD for BibXMLext, stored in the file <F>bibxmlext.dtd</F> which can
be found in the root directory of this &GAPDoc; package (and in Appendix
<Ref Appendix="bibxmlextdtd"/>):
For further details of the DTD we refer to the file <F>bibxmlext.dtd</F>
itself which is shown in appendix <Ref Appendix="bibxmlextdtd"/>. That
file also recalls some information from the &BibTeX; documentation on how
the standard fields of entries should be used. Which entry types and
which fields are supported (and the ordering of the fields which is
fixed by a DTD) can be either read off the DTD, or within &GAP; one can use
the function <Ref Func="TemplateBibXML"/> to get templates for the
various entry types.
<P/>
Here is an example of a BibXMLext document:
<Listing Type="doc/testbib.xml"><![CDATA[
<#Include SYSTEM "testbib.xml">
]]></Listing>
There is a standard XML header and a <C>DOCTYPE</C> declaration
referring to the <F>bibxmlext.dtd</F> DTD mentioned above. Local entities could be defined in the <C>DOCTYPE</C> tag as shown in the
example in <Ref Subsect="GDent"/>. The actual content of the document is
inside a <C><file></C>-element, it consists of <C><string></C>- and
<C><entry></C>-elements. Several of the BibXMLext markup features are
shown. We will use this input document for some examples below.
</Section>
<Section Label="BibXMLtools">
<Heading>Utilities for BibXMLext data</Heading>
<Subsection Label="Subsect:IntroXMLBib">
<Heading>Translating &BibTeX; to BibXMLext</Heading>
First we describe a tool which can translate bibliography entries from
&BibTeX; data to BibXMLext <C><entry></C>-elements. It also does some
validation of the data. In some
cases it is desirable to improve the result by hand afterwards
(editing formulae, adding <C><URL></C>-elements, translating
non-ASCII characters to unicode, ...).<P/>
See <Ref Func="WriteBibXMLextFile"/> below for how to write the results
to a BibXMLext file.
</Subsection>
<#Include Label="StringBibAsXMLext">
The following functions allow parsing of data which are already in
BibXMLext format.
<#Include Label="ParseBibXMLextString">
<#Include Label="WriteBibXMLextFile">
<Subsection Label="Subsect:RecBib">
<Heading>Bibliography Entries as Records</Heading>
For working with BibXMLext entries we find it convenient to first
translate the parse tree of an entry, as returned by <Ref
Func="ParseBibXMLextFiles"/>, to a record with the field names of the
entry as components whose value is the content of the field as string.
These strings are generated with respect to a result type. The records are
generated by the following function which can be customized by the user.
</Subsection>
<#Include Label="RecBibXMLEntry">
<#Include Label="AddHandlerBuildRecBibXMLEntry">
<#Include Label="StringBibXMLEntry">
The following command may be useful to generate completly new
bibliography entries in BibXMLext format. It also informs about the
supported entry types and field names.
<#Include Label="TemplateBibXML">
</Section>
<#Include Label="SearchMRSection">
</Chapter>
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