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>OLink Semantics in the DocBook DSSSL Stylesheets</TITLE
><META
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CLASS="ARTICLE"
BGCOLOR="#FFFFFF"
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><DIV
CLASS="ARTICLE"
><DIV
CLASS="TITLEPAGE"
><H1
CLASS="TITLE"
><A
NAME="AEN2"
>OLink Semantics in the DocBook DSSSL Stylesheets</A
></H1
><H3
CLASS="AUTHOR"
><A
NAME="AEN4"
>Norman Walsh</A
></H3
><P
CLASS="PUBDATE"
>10 Sep 1998<BR></P
><DIV
><DIV
CLASS="ABSTRACT"
><P
></P
><A
NAME="AEN8"
></A
><P
><CODE
CLASS="SGMLTAG"
>OLink</CODE
> allows you to construct cross-document links
in SGML. This document describes the <CODE
CLASS="SGMLTAG"
>OLink</CODE
> semantics supported
by the DocBook stylesheets.</P
><P
></P
></DIV
></DIV
><HR></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="OLINK-UNDERSTANDING"
>Understanding OLink</A
></H1
><P
>The semantics of <CODE
CLASS="SGMLTAG"
>OLink</CODE
> are effected by both the <CODE
CLASS="SGMLTAG"
>OLink</CODE
> tag and the <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> tag.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN18"
><CODE
CLASS="SGMLTAG"
>OLink</CODE
></A
></H2
><P
><CODE
CLASS="SGMLTAG"
>OLink</CODE
> is a wrapper around the text which forms the
head of the link. It has four relevant attributes:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
></DT
><DD
><P
>This <TT
CLASS="LITERAL"
>ENTITY</TT
> attribute points to the document which
is or contains the link target.</P
></DD
><DT
><CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
></DT
><DD
><P
>Contains the ID of the target in the document specified by <CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
>. <CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
> is the equivalent of <CODE
CLASS="SGMLTAG"
>LinkEnd</CODE
>
on the other linking elements.</P
></DD
><DT
><CODE
CLASS="SGMLTAG"
>LinkMode</CODE
></DT
><DD
><P
>Points to a <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> element which further modifies
the semantics of the link.</P
></DD
><DT
><CODE
CLASS="SGMLTAG"
>Type</CODE
></DT
><DD
><P
>Identifies the link type. The DocBook stylesheets include special processing
for <CODE
CLASS="SGMLTAG"
>Type</CODE
>=<TT
CLASS="LITERAL"
>href</TT
>.</P
><P
>If the link type is “href”, then the HREF attribute from
the <A
HREF="olinksemantics.html#OLINK-GENERAL"
>summary document</A
> is used directly,
without redirection through a CGI script.</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN53"
><CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
></A
></H2
><P
>An <CODE
CLASS="SGMLTAG"
>OLink</CODE
> element can refer to a <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> element to further modify the semantics of the link. Two aspects
of the <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> element are relevant:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
></DT
><DD
><P
>If the content of <CODE
CLASS="SGMLTAG"
>OLink</CODE
> is empty, it is possible
to use <CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
> to control the format
of generated text.</P
></DD
><DT
><CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> Content</DT
><DD
><P
>If the content of the <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> element is not empty,
it is used by the HTML stylesheet in the contruction of the HTML link “href”.</P
></DD
></DL
></DIV
></DIV
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="OLINK-HTML"
>OLinking in HTML</A
></H1
><P
>Constructing cross-document links with entities in the authoring system
is all well and good, but how does it work on the web? The heart of the matter
is mapping from the SGML/XML entity in the <CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
> to the base URL on the web, and there are two options: early binding
and late binding.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN78"
>Early Binding</A
></H2
><P
>To use early binding, you must know the mapping from entities to URLs
in advance. The base URL is supplied in the content of the <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> element and that is what the processor uses to construct the HTML
“href”. For example, given the document in <A
HREF="olinksemantics.html#EXAM1"
>Example 1</A
>,
the stylesheet would generate something like this for the link:</P
><PRE
CLASS="SCREEN"
><A CLASS="OLINK" HREF="http://nwalsh.com/otherdocs/myotherdoc.htm#idval">This
is an OLink</a></PRE
><P
>Note that the <CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
> is used
as the fragment identifier.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="EXAM1"
></A
><P
><B
>Example 1. An Early Binding Sample Document</B
></P
><PRE
CLASS="SCREEN"
><!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [
<!ENTITY otherdoc PUBLIC "-//Norman Walsh//DOCUMENT My Other Document V1.0//EN">
]>
<chapter>
<docinfo>
<modespec id=otherms>http://nwalsh.com/otherdocs/myotherdoc.htm</modespec>
</docinfo>
<title>Test Document</title>
<para>
<olink targetdocent=otherdoc linkmode="otherms" localinfo="idval">This is
an OLink</olink>.
</para>
</chapter></PRE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN89"
>Late Binding</A
></H2
><P
>Late binding delays the resolution of entity to URL mapping until the
link is followed. It does this by requiring that a web server process resolve
the link. “Out of the box,” the DocBook stylesheets assume that
a cgi-bin script on the server called <TT
CLASS="FILENAME"
>/cgi-bin/olink</TT
>
is responsible for the resolution.</P
><P
>Given the document in <A
HREF="olinksemantics.html#EXAM2"
>Example 2</A
>, late binding would produce
a link something like this:</P
><PRE
CLASS="SCREEN"
><A CLASS="OLINK" HREF="/cgi-bin/olink?pubid=-//Norman%20Walsh
//DOCUMENT%20My%20Other%20Document%20V1.0//EN&fragid=idval">
This is an OLink</a></PRE
><P
>(without the line break in the middle of the public identifier, of course).</P
><P
>Again, note that the <CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
>
is used as the fragment identifier.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="EXAM2"
></A
><P
><B
>Example 2. A Sample Document</B
></P
><PRE
CLASS="SCREEN"
><!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [
<!ENTITY otherdoc PUBLIC "-//Norman Walsh//DOCUMENT My Other Document V1.0//EN">
]>
<chapter>
<docinfo>
</docinfo>
<title>Test Document</title>
<para>
<olink targetdocent=otherdoc localinfo="idval">This is an OLink</olink>.
</para>
</chapter></PRE
></DIV
><P
>If a public identifier is used to declare the entity, then it is passed
to the link resolution script; otherwise the system identifier is passed.</P
></DIV
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN103"
>OLink Generated Text</A
></H1
><P
>Even when links span across documents, it's useful to have the stylesheet
generate appropriate cross-reference text. This greatly reduces the “fragility”
of the links at the expense of some complexity in the <CODE
CLASS="SGMLTAG"
>OLink</CODE
>
processing system.</P
><P
>If you supply content in an <CODE
CLASS="SGMLTAG"
>OLink</CODE
>, that content is
always used and generated text processing does not apply.</P
><P
>The format of generated text is controlled by the <CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
> attribute on the <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
> pointed to
by the <CODE
CLASS="SGMLTAG"
>OLink</CODE
>. The text of the <CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
> attribute is used for the generated text, with the following
substitutions:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>%g</TT
></DT
><DD
><P
>Is replaced by the “name” of the link target. This is generally
the “human readable” name of the target element. For example,
if the target is a <CODE
CLASS="SGMLTAG"
>Figure</CODE
>, <TT
CLASS="LITERAL"
>%g</TT
> would
be “Figure”; if the target is a <CODE
CLASS="SGMLTAG"
>Sect3</CODE
>, <TT
CLASS="LITERAL"
>%g</TT
> would be “Section”.</P
></DD
><DT
><TT
CLASS="LITERAL"
>%n</TT
></DT
><DD
><P
>Is replaced by the label (number) of the link target.</P
></DD
><DT
><TT
CLASS="LITERAL"
>%t</TT
></DT
><DD
><P
>Is replaced by the title of the link target.</P
></DD
></DL
></DIV
><P
>Suppose, for example, that the link target is the second section in
the first chapter of a book and that it has the title “My Test Title”.
If the <CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
> attribute contains the
text “<TT
CLASS="LITERAL"
>see %g %n, %t</TT
>”, then the generated content
would be “see Section 1.3, <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>My Test Title</I
></SPAN
>”.</P
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN138"
>Really Simple OLinks</A
></H1
><P
>If the author provides content in the <TT
CLASS="LITERAL"
>OLink</TT
> element,
that's the content that is used and no extra processing is required. The sections
that follow each deal with variations in the level of processing required
for generated text in <CODE
CLASS="SGMLTAG"
>OLink</CODE
>s.</P
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="OLINK-SIMPLE"
>Simple OLinks</A
></H1
><P
>Simple <CODE
CLASS="SGMLTAG"
>OLink</CODE
>s avoid some of the gory machinery required
to handle <A
HREF="olinksemantics.html#OLINK-GENERAL"
>general</A
> <CODE
CLASS="SGMLTAG"
>OLink</CODE
>s
at the expense of most semantic variation.</P
><P
>The simple semantics come into play when an <CODE
CLASS="SGMLTAG"
>OLink</CODE
>
has the following form:</P
><PRE
CLASS="SYNOPSIS"
><olink targetdocent="entity"></olink></PRE
><P
>In particular, note that there is no <CODE
CLASS="SGMLTAG"
>LinkMode</CODE
>. The generated text in this case is derived entirely from the public
and system identifiers by the <CODE
CLASS="FUNCTION"
>(olink-resource-title)</CODE
>
function. By default, this is simply the title of the document derived from
the description field in the public identifier. The first and last “words”
of the public identifier description field are trimmed off, leaving what is
presumably just the document title. For example, given “<TT
CLASS="LITERAL"
>-//Norman
Walsh//DOCUMENT My Document Title V1.0//EN</TT
>”, the derived title
would be “<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>My Document Title</I
></SPAN
>”.</P
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="OLINK-GENERAL"
>General OLinks</A
></H1
><P
>The generated text for general <CODE
CLASS="SGMLTAG"
>OLink</CODE
>s comes from
the <CODE
CLASS="SGMLTAG"
>XRefLabel</CODE
> attribute on the relevant <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
>. The hard part is locating the appropriate replacement
text: the name, label, and title of the element pointed to by the combination
of the <CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
> and <CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
>.</P
><P
>One way to do this would be to load the <CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
>, find the element with the ID mentioned in <CODE
CLASS="SGMLTAG"
>LocalInfo</CODE
> and extract the data directly. I chose
something else because I see two significant problems with this approach:</P
><P
></P
><OL
TYPE="1"
><LI
><P
>Loading and parsing potentially large documents potentially
many times appears to have the potential for significant performance problems.</P
></LI
><LI
><P
>It would not be possible to form <CODE
CLASS="SGMLTAG"
>OLink</CODE
>
references to documents written in DTDs other than DocBook.</P
></LI
></OL
><P
>Instead of loading the actual target document, the stylesheets load
a summary of that document's content. For DocBook documents, this summary
can be generated by another DSSSL stylesheet, <TT
CLASS="FILENAME"
>olink.dsl</TT
>,
supplied with the DocBook Stylesheet distribution. The first few lines of
the summary for this document is shown in looks like this:<A
HREF="olinksemantics.html#EXAM3"
>Example 3</A
>.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="EXAM3"
></A
><P
><B
>Example 3. OLink Summary Document</B
></P
><PRE
CLASS="PROGRAMLISTING"
><!DOCTYPE div PUBLIC "-//Norman Walsh//DTD DocBook OLink Summary V1.0//EN">
<div type="article" name="Article">
<ttl>OLink Semantics in the DocBook DSSSL Stylesheets</ttl>
<div type="sect1" name="Section" id="OLINK-UDERSTANDING" label="1">
<ttl>Understanding OLink</ttl>
<div type="sect2" name="Section" label="1.1">
<ttl>OLink</ttl>
</div>
...</PRE
></DIV
><P
>The basic organization of the summary document is a nested series of <CODE
CLASS="SGMLTAG"
>div</CODE
>s and <CODE
CLASS="SGMLTAG"
>obj</CODE
>s with titles (<CODE
CLASS="SGMLTAG"
>ttl</CODE
>s).
Attributes on these elements provide the IDs, labels, and names of the elements.
The GI of the element is also provided. (If you find objects that you think
are missing from the summary, please let me know).</P
><P
>The stylesheets locate this document by resolving the system identifier
of the target document and replacing the SGML or XML extension with <TT
CLASS="LITERAL"
>%olink-outline-ext%</TT
> (<TT
CLASS="LITERAL"
>.olink</TT
>, by default).</P
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN187"
>Intra-document OLinks</A
></H1
><P
>If the <CODE
CLASS="SGMLTAG"
>TargetDocEnt</CODE
> attribute is
missing, it seems reasonable to assume that the link refers to the current
document. This actually offers a feature, you can customize the generated
cross reference text for a particular reference.</P
><P
>When the <CODE
CLASS="SGMLTAG"
>OLink</CODE
> is an intra-document link, it is possible
to use additional %-substitutions in the cross reference template. See <CODE
CLASS="FUNCTION"
>(auto-xref)</CODE
> in <CODE
CLASS="SGMLTAG"
>dbcommon.dsl</CODE
> for more details.</P
></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN195"
>Examples</A
></H1
><P
>The examples that follow are all links into the document shown in <A
HREF="olinksemantics.html#FIG1"
>Figure 1</A
>.</P
><DIV
CLASS="FIGURE"
><A
NAME="FIG1"
></A
><P
><B
>Figure 1. Example Target Document</B
></P
><PRE
CLASS="PROGRAMLISTING"
><!DOCTYPE ARTICLE PUBLIC "-//OASIS//DTD DocBook V3.1//EN">
<article id="a1">
<?html-filename olinktarget.html>
<artheader>
<title>OLink Test Document</title>
</artheader>
<para>This document demonstrates cross-document linking with OLink. Format
this document with the <filename>olink.dsl</filename> stylesheet.</para>
<sect1 id="a1s1">
<title>A1 Section One</title>
<para>text</para>
</sect1>
<sect1 id="a1s2" xreflabel="Article Section Two">
<title>A1 <emphasis>Section</emphasis> Two</title>
<sect2 id="a1s1s1">
<title>A1 S1 Subsection One<superscript>1</superscript></title>
<para>text</para>
</sect2>
<sect2 id="a1s1s2">
<title>A1 S1 Subsection Two<subscript>2</subscript></title>
<para>text</para>
</sect2>
</sect1>
<sect1 id="a1s3">
<title>A1 Section Three</title>
<para>text</para>
</sect1>
</article></PRE
></DIV
><P
> The <CODE
CLASS="SGMLTAG"
>ModeSpec</CODE
>s in this document are shown in <A
HREF="olinksemantics.html#FIG2"
>Figure 2</A
>.</P
><DIV
CLASS="FIGURE"
><A
NAME="FIG2"
></A
><P
><B
>Figure 2. Example Target Document</B
></P
><PRE
CLASS="PROGRAMLISTING"
><modespec id=ms1 xreflabel="Name: '%g', Label: '%n', Title: '%t'"></modespec>
<modespec id=ms2 xreflabel="%g %n, %t"></modespec></PRE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN213"
></A
><P
><B
>Example 4. An OLink with Content</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><olink targetdocent=olinktarget>some text</olink></TT
></P
><P
>Result: <A
HREF="/cgi-bin/olink?pubid=-%2F%2FNorman%20Walsh%2F%2FDOCUMENT%20OLink%20Test%20Document%20V1.0%2F%2FEN"
CLASS="OLINK"
>some text</A
></P
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN219"
></A
><P
><B
>Example 5. A Simple OLink</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><olink targetdocent=olinktarget></olink></TT
></P
><P
>Result: <A
HREF="/cgi-bin/olink?pubid=-%2F%2FNorman%20Walsh%2F%2FDOCUMENT%20OLink%20Test%20Document%20V1.0%2F%2FEN"
CLASS="OLINK"
><I
>OLink Test Document</I
></A
></P
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN225"
></A
><P
><B
>Example 6. An OLink to a Document</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><olink targetdocent=olinktarget linkmode=ms1></olink></TT
></P
><P
>Result: <A
HREF="/cgi-bin/olink?pubid=-%2F%2FNorman%20Walsh%2F%2FDOCUMENT%20OLink%20Test%20Document%20V1.0%2F%2FEN"
CLASS="OLINK"
>Name: 'Article', Label: '', Title: '<I
>OLink Test Document</I
>'</A
></P
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN231"
></A
><P
><B
>Example 7. An OLink to a Section</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><olink targetdocent=olinktarget linkmode=ms2 localinfo=a1s2></olink></TT
></P
><P
>Result: <A
HREF="/cgi-bin/olink?pubid=-%2F%2FNorman%20Walsh%2F%2FDOCUMENT%20OLink%20Test%20Document%20V1.0%2F%2FEN&fragid=A1S2"
CLASS="OLINK"
>Section 2, <I
>Article Section Two</I
></A
></P
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN237"
></A
><P
><B
>Example 8. An Intra-Document OLink</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><olink linkmode=ms1 localinfo="olink-understanding"></olink></TT
></P
><P
>Result: <A
HREF="olinksemantics.html#OLINK-UNDERSTANDING"
CLASS="OLINK"
>Name: 'Section', Label: '', Title: '<I
>Understanding OLink</I
>'</A
></P
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN243"
></A
><P
><B
>Example 9. An XRef</B
></P
><P
>Source: <TT
CLASS="LITERAL"
><xref linkend="olink-understanding"></TT
></P
><P
>Result: <A
HREF="olinksemantics.html#OLINK-UNDERSTANDING"
>the Section called <I
>Understanding OLink</I
></A
></P
></DIV
></DIV
></DIV
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