1 <chapter id="introduction"><title>Introduction</title>
4 &yaz; is a C/C++ library for information retrieval applications
5 using the Z39.50/SRU protocols for information retrieval.
13 <ulink url="&url.z39.50;">Z39.50</ulink> version 3 support.
14 Amendments and Z39.50-2002 revision is supported.
18 <ulink url="&url.sru;">SRU GET/POST/SOAP</ulink>
19 version 1.1 (over HTTP and HTTPS).
22 Includes BER encoders/decoders for the
23 <ulink url="&url.ill;">ISO ILL</ulink>
27 Supports the following transports: BER over TCP/IP
28 (<ulink url="&url.ber.over.tcpip;">RFC1729</ulink>),
29 BER over unix local socket, and
30 <ulink url="&url.http.1.1;">HTTP 1.1</ulink>.
33 Secure Socket Layer support using
34 <ulink url="&url.openssl;">OpenSSL</ulink>.
35 If enabled, &yaz; uses HTTPS transport (for SOAP) or
36 "Secure BER" (for Z39.50).
40 <ulink url="&url.zoom;">ZOOM</ulink> C API implementing both
44 The &yaz; library offers a set of useful utilities
45 related to the protocols, such as MARC (ISO2709) parser,
47 <ulink url="&url.cql;">CQL</ulink>
48 parser, memory management routines, character set conversion.
51 Portable code. &yaz; compiles out-of-the box on most Unixes and
52 on Windows using Microsoft Visual C++.
55 Fast operation. The C based BER encoders/decoders as well
56 as the server component of &yaz; is very fast.
59 Liberal license that allows for commercial use of &yaz;.
64 <sect1 id="introduction.reading"><title>Reading this Manual</title>
65 <para>Most implementors only need to read a fraction of the
66 material in thie manual, so a quick walkthrough of the chapters
72 <xref linkend="installation"/> contains installation
73 instructions for &yaz;. You don't need reading this
74 if you expect to download &yaz; binaries.
75 However, the chapter contains information about how
76 to make <emphasis>your</emphasis> application link
83 <xref linkend="zoom"/> describes the ZOOM API of &yaz;.
84 This is definitely worth a read if you wish to develop a Z39.50/SRU
91 <xref linkend="server"/> describes the generic frontend server
92 and explains how to develop server Z39.50/SRU applications for &yaz;.
93 Obviously worth reading if you're to develop a server.
99 <xref linkend="yaz-client"/> describes how to use the &yaz; Z39.50
100 client. If you're developer and wish to test your server
101 or a server from another party, you might find this chapter
108 <xref linkend="asn"/> documents the most commonly used Z39.50
109 C data structures offered by the &yaz; API. Client
110 developers using ZOOM and non-Z39.50 implementors may skip this.
116 <xref linkend="soap"/> describes how SRU and SOAP is used
117 in &yaz;. Only if you're developing SRU applications
118 this section is a must.
124 <xref linkend="tools"/> contains sections for the various
125 tools offered by &yaz;. Scan through the material quickly
126 and see what's relevant to you! SRU implementors
127 might find the <link linkend="cql">CQL</link> section
134 <xref linkend="odr"/> goes through the details of the
135 ODR module which is the work horse that encodes and decodes
136 BER packages. Implementors using ZOOM only, do <emphasis>not</emphasis>
138 Most other Z39.50 implementors only need to read the first two
139 sections (<xref linkend="odr.introduction"/> and
140 <xref linkend="odr.use"/>).
146 <xref linkend="comstack"/> describes the network layer module
147 COMSTACK. Implementors using ZOOM or the generic frontend server
148 may skip this. Others, presumably, handling client/server
149 communication on their own should read this.
155 <sect1 id="introduction.api"><title>The API</title>
158 The <ulink url="&url.yaz;">&yaz;</ulink>
159 toolkit offers several different levels of access to the
160 <ulink url="&url.z39.50;">ISO23950/Z39.50</ulink>,
161 <ulink url="&url.ill;">ILL</ulink> and
162 <ulink url="&url.sru;">SRU</ulink>
164 The level that you need to use depends on your requirements, and
165 the role (server or client) that you want to implement.
166 If you're developing a client application you should consider the
167 <link linkend="zoom">ZOOM</link> API.
168 It is, by far, the easiest way to develop clients in C.
169 Server implementers should consider the
170 <link linkend="server">generic frontend server</link>.
171 None of those high-level APIs support the whole protocol, but
172 they do include most facilities used in existing Z39.50 applications.
175 If you're using 'exotic' functionality (meaning anything not included in
176 the high-level APIs), developing non-standard extensions to Z39.50 or
177 you're going to develop an ILL application you'll have to learn the lower
181 The YAZ toolkit modules is shown in figure <xref linkend="yaz.layer"/>.
183 <figure id="yaz.layer">
184 <title>YAZ layers</title>
187 <imagedata fileref="apilayer.png" format="PNG"/>
190 <imagedata fileref="apilayer.eps" format="EPS"/>
195 There are four layers.
198 <para>A client or server application (or both).
199 This layer includes ZOOM and the generic frontend server.
204 The second layer provides a C represenation of the
205 protocol units (packages) for Z39.50 ASN.1, ILL ASN.1,
211 The third layer encodes and decodes protocol data units to
212 simple packages (buffer with certain length). The &odr; module
213 encodes and decodes BER whereas the HTTP modules encodes and
214 decodes HTTP ruquests/responses.
219 The lowest layer is &comstack; which exchanges the encoded packages
220 with a peer process over a network.
226 The &asn; module represents the ASN.1 definition of
227 the Z39.50 protocol. It establishes a set of type and
228 structure definitions, with one structure for each of the top-level
229 PDUs, and one structure or type for each of the contained ASN.1 types.
230 For primitive types, or other types that are defined by the ASN.1
231 standard itself (such as the EXTERNAL type), the C representation is
232 provided by the &odr; (Open Data Representation) subsystem.
235 &odr; is a basic mechanism for representing an
236 ASN.1 type in the C programming language, and for implementing BER
237 encoders and decoders for values of that type. The types defined in
238 the &asn; module generally have the prefix <literal>Z_</literal>, and
239 a suffix corresponding to the name of the type in the ASN.1
240 specification of the protocol (generally Z39.50-1995). In the case of
241 base types (those originating in the ASN.1 standard itself), the prefix
242 <literal>Odr_</literal> is sometimes seen. Either way, look for
243 the actual definition in either <filename>z-core.h</filename> (for the types
244 from the protocol), <filename>odr.h</filename> (for the primitive ASN.1
246 The &asn; library also provides functions (which are, in turn,
247 defined using &odr; primitives) for encoding and decoding data values.
248 Their general form is
251 <funcprototype><funcdef>int <function>z_<replaceable>xxx</replaceable></function></funcdef>
252 <paramdef>ODR <parameter>o</parameter></paramdef>
253 <paramdef>Z_<replaceable>xxx</replaceable> **<parameter>p</parameter></paramdef>
254 <paramdef>int <parameter>optional</parameter></paramdef>
255 <paramdef>const char *<parameter>name</parameter></paramdef>
258 (note the lower-case "z" in the function name)
263 If you are using the premade definitions of the &asn; module, and you
264 are not adding new protocol of your own, the only parts of &odr; that you
265 need to worry about are documented in
266 <xref linkend="odr.use"/>.
271 When you have created a BER-encoded buffer, you can use the &comstack;
272 subsystem to transmit (or receive) data over the network. The &comstack;
273 module provides simple functions for establishing a connection
274 (passively or actively, depending on the role of your application),
275 and for exchanging BER-encoded PDUs over that connection. When you
276 create a connection endpoint, you need to specify what transport to
277 use (TCP/IP, SSL or UNIX sockets).
278 For the remainder of the connection's lifetime, you don't have
279 to worry about the underlying transport protocol at all - the &comstack;
280 will ensure that the correct mechanism is used.
283 We call the combined interfaces to &odr;, &asn;, and &comstack; the service
284 level API. It's the API that most closely models the Z39.50
285 service/protocol definition, and it provides unlimited access to all
286 fields and facilities of the protocol definitions.
289 The reason that the &yaz; service-level API is a conglomerate of the
290 APIs from three different submodules is twofold. First, we wanted to allow
291 the user a choice of different options for each major task. For instance,
292 if you don't like the protocol API provided by &odr;/&asn;, you
293 can use SNACC or BERUtils instead, and still have the benefits of the
294 transparent transport approach of the &comstack; module. Secondly,
295 we realize that you may have to fit the toolkit into an existing
296 event-processing structure, in a way that is incompatible with
297 the &comstack; interface or some other part of &yaz;.
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