- Zebra is born as a networking Information Retrieval engine adhering
- to the international standards
- <ulink url="&url.z39.50;">Z39.50</ulink> and
- <ulink url="&url.sru;">SRU</ulink>,
- and implement the query model defined there.
- Unfortunately, the Z39.50 query model has only defined a binary
- encoded representation, which is used as transport packaging in
- the Z39.50 protocol layer. This representation is not human
- readable, nor defines any convenient way to specify queries.
- </para>
- <para>
- Therefore, Index Data has defined a textual representaion in the
- <literal>Prefix Query Format</literal>, short
- <literal>PQF</literal>, which then has been adopted by other
- parties developing Z39.50 software. It is also often referred to as
- <literal>Prefix Query Notation</literal>, or in short
- <literal>PQN</literal>, and is thoroughly explained in
- <xref linkend="querymodel-pqf"/>.
- </para>
-
- <para>
- In addition, Zebra can be configured to understand and map the
- <literal>Common Query Language</literal>
- (<ulink url="&url.cql;">CQL</ulink>)
- to PQF. See an introduction on the mapping to the internal query
- representation in
- <xref linkend="querymodel-cql-to-pqf"/>.
- </para>
- </sect1>
+ Index Data has defined a textual representaion in the
+ <literal>Prefix Query Format</literal>, short
+ <literal>PQF</literal>, which mappes
+ <literal>one-to-one</literal> to binary encoded
+ <literal>type-1 RPN</literal> query packages.
+ It has been adopted by other
+ parties developing Z39.50 software, and is often referred to as
+ <literal>Prefix Query Notation</literal>, or in short
+ <literal>PQN</literal>. See
+ <xref linkend="querymodel-pqf"/> for further explanaitions and
+ descriptions of Zebra's capabilities.
+ </para>
+ </sect3>
+
+ <sect3 id="querymodel-query-languages-cql">
+ <title>Common Query Language (CQL)</title>
+ <para>
+ The query model of the <literal>type-1 RPN</literal>,
+ expressed in <literal>PQF/PQN</literal> is natively supported.
+ On the other hand, the default <literal>SRU</literal>
+ webservices <literal>Common Query Language</literal>
+ <ulink url="&url.cql;">CQL</ulink> is not natively supported.
+ </para>
+ <para>
+ Zebra can be configured to understand and map CQL to PQF. See
+ <xref linkend="querymodel-cql-to-pqf"/>.
+ </para>
+ </sect3>
+
+ </sect2>
+
+ <sect2 id="querymodel-operation-types">
+ <title>Operation types</title>
+ <para>
+ Zebra supports all of the three different
+ <literal>Z39.50/SRU</literal> operations defined in the
+ standards: <literal>explain</literal>, <literal>search</literal>,
+ and <literal>scan</literal>. A short description of the
+ functionality and purpose of each is quite in order here.
+ </para>
+
+ <sect3 id="querymodel-operation-type-explain">
+ <title>Explain Operation</title>
+ <para>
+ The <emphasis>syntax</emphasis> of Z39.50/SRU queries is
+ well known to any client, but the specific
+ <emphasis>semantics</emphasis> - taking into account a
+ particular servers functionalities and abilities - must be
+ discovered from case to case. Enters the
+ <literal>explain</literal> operation, which provides the means
+ for learning which
+ <emphasis>fields</emphasis> (also called
+ <emphasis>indexes</emphasis> or <emphasis>access points</emphasis>
+ are provided, which default parameter the server uses, which
+ retrieve document formats are defined, and which specific parts
+ of the general query model are supported.
+ </para>
+ <para>
+ The Z39.50 embeddes the <literal>explain</literal> operation
+ by perfoming a
+ <literal>search</literal> in the magic
+ <literal>IR-Explain-1</literal> database;
+ see <xref linkend="querymodel-exp1"/>.
+ </para>
+ <para>
+ In SRU, <literal>explain</literal> is an entirely seperate
+ operation, which returns an <literal>Zeerex
+ XML</literal> record according to the
+ structure defined by the protocol.
+ </para>
+ <para>
+ In both cases, the information gathered through
+ <literal>explain</literal> operations can be used to
+ auto-configure a client user interface to the servers
+ capabilities.
+ </para>
+ </sect3>
+
+ <sect3 id="querymodel-operation-type-search">
+ <title>Search Operation</title>
+ <para>
+ Search and retrieve interactions are the raison d'être.
+ They are used to query the remote database and
+ return search result documents. Search queries span from
+ simple free text searches to nested complex boolean queries,
+ targeting specific indexes, and possibly enhanced with many
+ query semantic specifications. Search interactions are the heart
+ and soul of Z39.50/SRU servers.
+ </para>
+ </sect3>
+
+ <sect3 id="querymodel-operation-type-scan">
+ <title>Scan Operation</title>
+ <para>
+ The <literal>scan</literal> operation is a helper functionality,
+ which operates on one index or access point a time.
+ </para>
+ <para>
+ It provides
+ the means to investigate the content of specific indexes.
+ Scanning an index returns a handfull of terms actually fond in
+ the indexes, and in addition the <literal>scan</literal>
+ operation returns th enumber of documents indexed by each term.
+ A search client can use this information to propose proper
+ spelling of search terms, to auto-fill search boxes, or to
+ display controlled vocabularies.
+ </para>
+ </sect3>
+
+ </sect2>
+
+ </sect1>
+
projects / idzebra-moved-to-github.git / blobdiff