YAZ version 2.1.20 or later includes a Retrieval facility tool which allows a SRU/Z39.50 to describe itself and perform record conversions. The idea is the following:
An SRU/Z39.50 client sends a retrieval request which includes a combination of the following parameters: syntax (format), schema (or element set name).
The retrieval facility is invoked with parameters in a server/proxy. The retrieval facility matches the parameters a set of "supported" retrieval types. If there is no match, the retrieval signals an error (syntax and / or schema not supported).
For a successful match, the backend is invoked with the same or altered retrieval parameters (syntax, schema). If a record is received from the backend, it is converted to the frontend name / syntax.
The resulting record is sent back the client and tagged with the frontend syntax / schema.
The Retrieval facility is driven by an XML configuration. The configuration is neither Z39.50 ZeeRex or SRU ZeeRex. But it should be easy to generate both of them from the XML configuration. (Unfortunately the two versions of ZeeRex differ substantially in this regard.)
All elements should be covered by namespace
http://indexdata.com/yaz .
The root element node must be retrievalinfo.
The retrievalinfo must include one or
more retrieval elements. Each
retrieval defines specific combination of
syntax, name and identifier supported by this retrieval service.
The retrieval element may include any of the
following attributes:
syntax (REQUIRED)Defines the record syntax. Possible values is any of the names defined in YAZ' OID database or a raw OID in (n.n ... n).
name (OPTIONAL)
Defines the name of the retrieval format. This can be
any string. For SRU, the value is equivalent to schema (short-hand);
for Z39.50 it's equivalent to simple element set name.
For YAZ 3.0.24 and later this name may be specified as a glob
expression with operators
* and ?.
identifier (OPTIONAL)Defines the URI schema name of the retrieval format. This can be any string. For SRU, the value is equivalent to URI schema. For Z39.50, there is no equivalent.
The retrieval may include one
backend element. If a backend
element is given, it specifies how the records are retrieved by
some backend and how the records are converted from the backend to
the "frontend".
The attributes, name and syntax
may be specified for the backend element. The
semantics of these attributes is equivalent to those for the
retrieval. However, these values are passed to
the "backend".
The backend element may include one or more
conversion instructions (as children elements). The supported
conversions are:
marc
The marc element specifies a conversion
to - and from ISO2709 encoded MARC and
MARCXML/MarcXchange.
The following attributes may be specified:
inputformat (REQUIRED)
Format of input. Supported values are
marc (for ISO2709), xml
(MARCXML/MarcXchange) and json
(MARC-in-JSON).
outputformat (REQUIRED)
Format of output. Supported values are
line (MARC line format);
marcxml (for MARCXML),
marc (ISO2709),
marcxhcange (for MarcXchange),
or json
(MARC-in-JSON ).
inputcharset (OPTIONAL)
Encoding of input. For XML input formats, this need not
be given, but for ISO2709 based inputformats, this should
be set to the encoding used. For MARC21 records, a common
inputcharset value would be marc-8.
outputcharset (OPTIONAL)
Encoding of output. If outputformat is XML based, it is
strongly recommened to use utf-8.
select
The select selects one or more text nodes
and decodes them as XML.
The following attributes may be specified:
path (REQUIRED)X-Path expression for selecting text nodes.
This conversion is available in YAZ 5.8.0 and later.
solrmarc
The solrmarc decodes solrmarc records.
It assumes that the input is pure solrmarc text (no escaping)
and will convert all sequences of the form #XX; to a single
character of the hexadecimal value as given by XX. The output,
presumably, is a valid ISO2709 buffer.
This conversion is available in YAZ 5.0.21 and later.
xslt
The xslt element specifies a conversion
via XSLT. The following attributes may be specified:
stylesheet (REQUIRED)Stylesheet file.
Example 7.19. MARC21 backend
A typical way to use the retrieval facility is to enable XML for servers that only supports ISO2709 encoded MARC21 records.
<retrievalinfo>
<retrieval syntax="usmarc" name="F"/>
<retrieval syntax="usmarc" name="B"/>
<retrieval syntax="xml" name="marcxml"
identifier="info:srw/schema/1/marcxml-v1.1">
<backend syntax="usmarc" name="F">
<marc inputformat="marc" outputformat="marcxml"
inputcharset="marc-8"/>
</backend>
</retrieval>
<retrieval syntax="xml" name="dc">
<backend syntax="usmarc" name="F">
<marc inputformat="marc" outputformat="marcxml"
inputcharset="marc-8"/>
<xslt stylesheet="MARC21slim2DC.xsl"/>
</backend>
</retrieval>
</retrievalinfo>
This means that our frontend supports:
MARC21 F(ull) records.
MARC21 B(rief) records.
MARCXML records.
Dublin core records.
Example 7.20. MARCXML backend
SRW/SRU and Solr backends return records in XML. If they return MARCXML or MarcXchange, the retrieval module can convert those into ISO2709 formats, most commonly USMARC (AKA MARC21). In this example, the backend returns MARCXML for schema="marcxml".
<retrievalinfo>
<retrieval syntax="usmarc">
<backend syntax="xml" name="marcxml">
<marc inputformat="xml" outputformat="marc"
outputcharset="marc-8"/>
</backend>
</retrieval>
<retrieval syntax="xml" name="marcxml"
identifier="info:srw/schema/1/marcxml-v1.1"/>
<retrieval syntax="xml" name="dc">
<backend syntax="xml" name="marcxml">
<xslt stylesheet="MARC21slim2DC.xsl"/>
</backend>
</retrieval>
</retrievalinfo>
This means that our frontend supports:
MARC21 records (any element set name) in MARC-8 encoding.
MARCXML records for element-set=marcxml
Dublin core records for element-set=dc.