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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>2.The API</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"><link rel="home" href="index.html" title="YAZ User's Guide and Reference"><link rel="up" href="introduction.html" title="Chapter1.Introduction"><link rel="prev" href="introduction.html" title="Chapter1.Introduction"><link rel="next" href="installation.html" title="Chapter2.Compilation and Installation"></head><body><link rel="stylesheet" type="text/css" href="common/style1.css"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.The API</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="introduction.html">Prev</a></td><th width="60%" align="center">Chapter1.Introduction</th><td width="20%" align="right"><a accesskey="n" href="installation.html">Next</a></td></tr></table><hr></div><div class="sect1" title="2.The API"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="introduction.api"></a>2.The API</h2></div></div></div><p>
The <a class="ulink" href="http://www.indexdata.com/yaz" target="_top">YAZ</a>
toolkit offers several different levels of access to the
<a class="ulink" href="http://www.loc.gov/z3950/agency/" target="_top">ISO23950/Z39.50</a>,
<a class="ulink" href="http://www.nlc-bnc.ca/iso/ill/" target="_top">ILL</a> and
<a class="ulink" href="http://www.loc.gov/standards/sru/" target="_top">SRU</a>
protocols.
The level that you need to use depends on your requirements, and
the role (server or client) that you want to implement.
If you're developing a client application you should consider the
<a class="link" href="zoom.html" title="Chapter3.ZOOM">ZOOM</a> API.
It is, by far, the easiest way to develop clients in C.
Server implementers should consider the
<a class="link" href="server.html" title="Chapter4.Generic server">generic frontend server</a>.
None of those high-level APIs support the whole protocol, but
they do include most facilities used in existing Z39.50 applications.
</p><p>
If you're using 'exotic' functionality (meaning anything not included in
the high-level APIs), developing non-standard extensions to Z39.50 or
you're going to develop an ILL application you'll have to learn the lower
level APIs of YAZ.
</p><p>
The YAZ toolkit modules is shown in figure <a class="xref" href="introduction.api.html#yaz.layer" title="Figure1.1.YAZ layers">Figure1.1, “YAZ layers”</a>.
</p><div class="figure"><a name="yaz.layer"></a><p class="title"><b>Figure1.1.YAZ layers</b></p><div class="figure-contents"><div class="mediaobject"><img src="apilayer.png" alt="YAZ layers"></div></div></div><br class="figure-break"><p>
There are four layers.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>A client or server application (or both).
This layer includes ZOOM and the generic frontend server.
</p></li><li class="listitem"><p>
The second layer provides a C represenation of the
protocol units (packages) for Z39.50 ASN.1, ILL ASN.1,
SRU.
</p></li><li class="listitem"><p>
The third layer encodes and decodes protocol data units to
simple packages (buffer with certain length). The <acronym class="acronym">ODR</acronym> module
encodes and decodes BER whereas the HTTP modules encodes and
decodes HTTP ruquests/responses.
</p></li><li class="listitem"><p>
The lowest layer is <acronym class="acronym">COMSTACK</acronym> which exchanges the encoded packages
with a peer process over a network.
</p></li></ul></div><p>
</p><p>
The Z39.50 ASN.1 module represents the ASN.1 definition of
the Z39.50 protocol. It establishes a set of type and
structure definitions, with one structure for each of the top-level
PDUs, and one structure or type for each of the contained ASN.1 types.
For primitive types, or other types that are defined by the ASN.1
standard itself (such as the EXTERNAL type), the C representation is
provided by the <acronym class="acronym">ODR</acronym> (Open Data Representation) subsystem.
</p><p>
<acronym class="acronym">ODR</acronym> is a basic mechanism for representing an
ASN.1 type in the C programming language, and for implementing BER
encoders and decoders for values of that type. The types defined in
the Z39.50 ASN.1 module generally have the prefix <code class="literal">Z_</code>, and
a suffix corresponding to the name of the type in the ASN.1
specification of the protocol (generally Z39.50-1995). In the case of
base types (those originating in the ASN.1 standard itself), the prefix
<code class="literal">Odr_</code> is sometimes seen. Either way, look for
the actual definition in either <code class="filename">z-core.h</code> (for the types
from the protocol), <code class="filename">odr.h</code> (for the primitive ASN.1
types).
The Z39.50 ASN.1 library also provides functions (which are, in turn,
defined using <acronym class="acronym">ODR</acronym> primitives) for encoding and decoding data values.
Their general form is
</p><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">z_xxx</b>(</code></td><td><var class="pdparam">o</var>, </td><td></td></tr><tr><td></td><td><var class="pdparam">p</var>, </td><td></td></tr><tr><td></td><td><var class="pdparam">optional</var>, </td><td></td></tr><tr><td></td><td><var class="pdparam">name</var><code>)</code>;</td><td></td></tr></table><div class="paramdef-list"><code>ODR <var class="pdparam">o</var></code>;<br><code>Z_xxx **<var class="pdparam">p</var></code>;<br><code>int <var class="pdparam">optional</var></code>;<br><code>const char *<var class="pdparam">name</var></code>;</div><div class="funcprototype-spacer"></div></div><p>
(note the lower-case "z" in the function name)
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
If you are using the premade definitions of the Z39.50 ASN.1 module, and you
are not adding new protocol of your own, the only parts of <acronym class="acronym">ODR</acronym> that you
need to worry about are documented in
<a class="xref" href="odr.use.html" title="2.Using ODR">Section2, “Using ODR”</a>.
</p></div><p>
When you have created a BER-encoded buffer, you can use the <acronym class="acronym">COMSTACK</acronym>
subsystem to transmit (or receive) data over the network. The <acronym class="acronym">COMSTACK</acronym>
module provides simple functions for establishing a connection
(passively or actively, depending on the role of your application),
and for exchanging BER-encoded PDUs over that connection. When you
create a connection endpoint, you need to specify what transport to
use (TCP/IP, SSL or UNIX sockets).
For the remainder of the connection's lifetime, you don't have
to worry about the underlying transport protocol at all - the <acronym class="acronym">COMSTACK</acronym>
will ensure that the correct mechanism is used.
</p><p>
We call the combined interfaces to <acronym class="acronym">ODR</acronym>, Z39.50 ASN.1, and <acronym class="acronym">COMSTACK</acronym> the service
level API. It's the API that most closely models the Z39.50
service/protocol definition, and it provides unlimited access to all
fields and facilities of the protocol definitions.
</p><p>
The reason that the YAZ service-level API is a conglomerate of the
APIs from three different submodules is twofold. First, we wanted to allow
the user a choice of different options for each major task. For instance,
if you don't like the protocol API provided by <acronym class="acronym">ODR</acronym>/Z39.50 ASN.1, you
can use SNACC or BERUtils instead, and still have the benefits of the
transparent transport approach of the <acronym class="acronym">COMSTACK</acronym> module. Secondly,
we realize that you may have to fit the toolkit into an existing
event-processing structure, in a way that is incompatible with
the <acronym class="acronym">COMSTACK</acronym> interface or some other part of YAZ.
</p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="introduction.html">Prev</a></td><td width="20%" align="center"><a accesskey="u" href="introduction.html">Up</a></td><td width="40%" align="right"><a accesskey="n" href="installation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter1.Introduction</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">Chapter2.Compilation and Installation</td></tr></table></div></body></html>
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