Specifying and Using Application (Database) Profiles
Index Data, info@indexdata.dk
$Revision$
YAZ includes a subsystem to manage complex database records, driven by
a set of configuration tables that reflect a given profile. Multiple
database profiles can coexeist in the same server, or even the same
database. The record management system is responsible for associating
a given record with a specific profile, and processing it accordingly.
This document describes the various file formats for data and configu-
ration files which are used by the module.
______________________________________________________________________
Table of Contents
1. Warnings
2. Introduction
3. Overview
3.1 External Data (record) Representation
3.2 The Abstract Syntax
4. The Configuration Files
4.1 The Abstract Syntax (.abs) Files
4.2 The Attribute Set (.att) Files
4.3 The Tag Set (.tag) Files
4.4 The Variant Set (.var) Files
4.5 The Element Set (.est) Files
4.6 The Schema Mapping (.map) Files
4.7 The MARC (ISO2709) Representation (.mar) Files
5. The Input (Data) File Format
6. License
7. About Index Data
______________________________________________________________________
1. Warnings
o The subsystem descibed herein is under development. Not everything
may work exactly as decribed, and details of the interface may
change as the module matures.
o The exact workings of the subsystem may depend on the application
in which it is used. This document focuses on the use of the module
in the Zebra information server which is distributed by Index Data
as an independent package.
2. Introduction
The retrieval facilities of Z39.50 are extremely flexible and
powerful. They allow any level of structuring of database records.
They allow controlled re-use of attribute sets (for searching) and tag
sets (for retrieval) between application profiles; they allow precise
selection of the desired sub-elements of a database record; they allow
different variants of a given data element to be represented and
selected in a structured way; and finally they allow the exchange of
any type and amount of data to be represented in a single database
record.
These powerful retrieval facilities are a recent addition to the
protocol, and along with the flexible searching facilities, they make
the protocol an extremely capable tool for precise, structured access
to information systems. The retrieval facilities add new levels of
flexibility and control to the protocol, which add to its value
outside of its traditional domain of the library systems world.
The new facilities, however, also add new complexity to the protocol,
which is already troubles by a too-steep learning curve. We have seen
many good projects severely hindered or even thwarted by the sheer
complexity of implementing the Z39.50 protocol.
At the same time, we feel that the most complex and powerful
facilities of the protocol (Explain, structured retrieval, etc.), are
also what the protocol needs to become more widespread, and to fulfill
what we perceive to be its most noble potential: To provide everybody
with standardised, well-structured access to the information resources
of the world.
The purpose of YAZ, then, and of this module as well, is to simplify
the use of the protocol for programmers and administrators, by
providing simple APIs and configuration systems to access the
functionality of the protocol. The Retrieval module deals specifically
with the advanced retrieval functions which were added to the protocol
with version 3, or Z39.50-1994.
3. Overview
3.1. External Data (record) Representation
The Retrieval module will eventually support a wide range of input
formats, ranging from MARC data to USENET news archives. This section
introduces what we think of as the canonical format - the one that
gives the most general access to the various elements of the retrieval
functionality.
The basic model presented by the Z39.50 retrieval system is that of a
recursively defined tree structure, containing a list of tagged
elements, which may in turn contain either data or more lists of
tagged elements, and so forth.
We elect to represent this structuring externally by using an "SGML-
like" syntax. The internal representation will be discussed later.
Consider a record describing an information resource (such a record is
sometimes known as a locator record). It might contain a field
describing the distributor of the information resource, which might in
turn be partitioned into various fields providing details about the
distributor, like this:
USGS/WRD
USGS/WRD
U.S. GEOLOGICAL SURVEY, 505 MARQUETTE, NW
ALBUQUERQUE
NM
87102
USA
(505) 766-5560
This is how data that the retrieval module reads from an input file
might look.
Depending on the database profile that is being used, it is likely
that the data won't look like this when it's transmitted from the
server to the client, however. Typically, the client will prefer to
receive the data in a more rigid syntax, such as USMARC or GRS-1. To
save transmission time and avoid ambiguities of language, the
individual tags or field names, above, might be translated into
numbers which are known by both the client and the server (by
referring to a tag set).
The retrieval module supports various types of conversions that might
be carried out by the server based on requests from the client. To do
this, it needs a set of configuration files to describe the
application profile that the given record adheres to.
CAUTION: Because the tables described below serve the dual purpose of
representing an external application profile and an internal database
profile, the terminology and structuring used will sometimes be
somewhat different from the one suggested in the the Z39.50-1995.
3.2. The Abstract Syntax
The abstract syntax definition (ARS) is the focal point of the
application profile description. For a given profile, it may state any
or all of the following:
o The object identifier of the database schema associated with the
profile, so that it can be referred to by the client.
o The attribute set (which can possibly be a compound of multiple
sets) which applies in the profile. This is used when indexing and
searching the records belonging to the given profile.
o The Tag set (again, this can consist of several different sets).
This is used when reading the records from a file, to recognize the
different tags, and when transmitting the record to the client -
mapping the tags to their numerical representation, if they are
known.
o The variant set which is used in the profile. This provides a
vocabulary for specifying the forms of data that appear inside the
records.
o Element set names, which are a shorthand way for the client to ask
for a subset of the data elements contained in a record. Element
set names, in the retrieval module, are mapped to element
specifications, which contain information equivalent to the Espec-1
syntax of Z39.50.
o Map tables, which may specify mappings to other database profiles,
if desired.
o Possibly, a set of rules describing the mapping of elements to a
MARC representation.
o A list of element description (this is the actual ARS of the
profile), which lists the ways in which the various tags can be
used and organized hierarchically.
Several of the entries above simply refer to other files, which
describe the given objects.
4. The Configuration Files
This section describes the syntax and use of the various tables which
are used by the retrieval module.
The number of different file types may appear daunting at first, but
each type corresponds fairly clearly to a single aspect of the Z39.50
retrieval facilities. Further, the average database administrator
who's simply reusing an existing profile for which tables already
exist, shouldn't have to worry too much about these tables.
4.1. The Abstract Syntax (.abs) Files
The name of this file type is slightly misleading, since, apart from
the actual abstract syntax of the profile, it also includes most of
the other definitions that go into a database profile.
When a record in the canonical, SGML-like format is read from a file
or from the database, the first tag of the file should reference the
profile that governs the layout of the record. If the first tag of the
record is , the system will look for the profile definition in
the file gils.abs. Profile definitions are cached, so they only have
to be read once during the lifespan of the current process.
The file may contain the following directives:
name symbolic-name
This provides a shorthand name or description for the profile.
Mostly useful for diagnostic purposes.
reference OID-name
The reference name of the OID for the profile. The reference
names can be found in the util module of YAZ.
attset filename
The attribute set that is used for indexing and searching
records belonging to this profile.
tagset filename
The tag set (if any) that describe that fields of the records.
varset filename
The variant set used in the profile.
maptab filename
(repeatable) This points to a conversion table that might be
used if the client asks for the record in a different schema
from the native one.
marc filename
Points to a file containing parameters for representing the
record contents in the ISO2709 syntax. Read the description of
the MARC representation facility below.
esetname name filename
(repeatable) Associates the given element set name with an
element selection file. If an (@) is given in place of the
filename, this corresponds to a null mapping for the given
element set name.
elm path name attribute
(repeatable) Adds an element to the abstract record syntax of
the schema. The path follows the syntax which is suggested by
the Z39.50 document - that is, a sequence of tags separated by
slashes (/). Each tag is given as a comma-separated pair of tag
type and -value surrounded by parenthesis. The name is the name
of the element, and the attribute specifies what attribute to
use when indexing the element. A ! in place of the attribute
name is equivalent to specifying an attribute name identical to
the element name. A - in place of the attribute name specifies
that no indexing is to take place for the given element.
NOTE: The mechanism for controlling indexing is inadequate for complex
databases, and will probably be moved into a separate configuration
table eventually.
The following is an excerpt from the abstract syntax file for the GILS
profile.
name gils
reference GILS-schema
attset gils.att
tagset gils.tag
varset var1.var
maptab gils-usmarc.map
# Element set names
esetname VARIANT gils-variant.est # for WAIS-compliance
esetname B gils-b.est
esetname G gils-g.est
esetname W gils-b.est
esetname F @
elm (1,10) rank -
elm (1,12) url -
elm (1,14) localControlNumber Local-number
elm (1,16) dateOfLastModification Date/time-last-modified
elm (2,1) Title !
elm (4,1) controlIdentifier Identifier-standard
elm (2,6) abstract Abstract
elm (4,51) purpose !
elm (4,52) originator -
elm (4,53) accessConstraints !
elm (4,54) useConstraints !
elm (4,70) availability -
elm (4,70)/(4,90) distributor -
elm (4,70)/(4,90)/(2,7) distributorName !
elm (4,70)/(4,90)/(2,10 distributorOrganization !
elm (4,70)/(4,90)/(4,2) distributorStreetAddress !
elm (4,70)/(4,90)/(4,3) distributorCity !
4.2. The Attribute Set (.att) Files
This file type describes the Use elements of an attribute set. It
contains the following directives.
name symbolic-name
This provides a shorthand name or description for the attribute
set. Mostly useful for diagnostic purposes.
reference OID-name
The reference name of the OID for the attribute set. The
reference names can be found in the util module of YAZ.
ordinal integer
This value will be used to represent the attribute set in the
index. Care should be taken that each attribute set has a unique
ordinal value.
include filename
This directive, which can be repeated, is used to include
another attribute set as a part of the current one. This is used
when a new attribute set is defined as an extension to another
set. For instance, many new attribute sets are defined as
extensions to the bib-1 set. This is an important feature of the
retrieval system of Z39.50, as it ensures the highest possible
level of interoperability, as those access points of your
database which are derived from the external set (say, bib-1)
can be used even by clients who are unaware of the new set.
att att-value att-name [local-value]
This repeatable directive introduces a new attribute to the set.
The attribute value is stored in the index (unless a local-value
is given, in which case this is stored). The name is used to
refer to the attribute from the abstract syntax.
This is an excerpt from the GILS attribute set definition. Notice how
the file describing the bib-1 attribute set is referenced.
name gils
reference GILS-attset
include bib1.att
ordinal 2
att 2001 distributorName
att 2002 indexTermsControlled
att 2003 purpose
att 2004 accessConstraints
att 2005 useConstraints
4.3. The Tag Set (.tag) Files
This file type defines the tagset of the profile, possibly by
referencing other tag sets (most tag sets, for instance, will include
tagsetG and tagsetM from the Z39.50 specification. The file may
contain the following directives.
name symbolic-name
This provides a shorthand name or description for the tag set.
Mostly useful for diagnostic purposes.
reference OID-name
The reference name of the OID for the tag set. The reference
names can be found in the util module of YAZ.
type integer
The type number of the tag within the schema profile.
include filename
(repeatable) This directive is used to include the definitions
of other tag sets into the current one.
tag number names type
(repeatable) Introduces a new tag to the set. The number is the
tag number as used in the protocol (there is currently no
mechanism for specifying string tags at this point, but this
would be quick work to add). The names parameter is a list of
names by which the tag should be recognized in the input file
format. The names should be separated by slashes (/). The type
is th recommended datatype of the tag. It should be one of the
following:
o structured
o string
o numeric
o bool
o oid
o generalizedtime
o intunit
o int
o octetstring
o null
The following is an excerpt from the TagsetG definition file.
name tagsetg
reference TagsetG
type 2
tag 1 title string
tag 2 author string
tag 3 publicationPlace string
tag 4 publicationDate string
tag 5 documentId string
tag 6 abstract string
tag 7 name string
tag 8 date generalizedtime
tag 9 bodyOfDisplay string
tag 10 organization string
4.4. The Variant Set (.var) Files
The variant set file is a straightforward representation of the
variant set definitions associated with the protocol. At present, only
the Variant-1 set is known.
These are the directives allowed in the file.
name symbolic-name
This provides a shorthand name or description for the variant
set. Mostly useful for diagnostic purposes.
reference OID-name
The reference name of the OID for the variant set, if one is
required. The reference names can be found in the util module of
YAZ.
class integer class-name
(repeatable) Introduces a new class to the variant set.
type integer type-name datatype
(repeatable) Addes a new type to the current class (the one
introduced by the most recent class directive). The type names
belong to the same name space as the one used in the tag set
definition file.
The following is an excerpt from the file describing the variant set
Variant-1.
name variant-1
reference Variant-1
class 1 variantId
type 1 variantId octetstring
class 2 body
type 1 iana string
type 2 z39.50 string
type 3 other string
4.5. The Element Set (.est) Files
The element set specification files describe a selection of a subset
of the elements of a database record. The element selection mechanism
is equivalent to the one supplied by the Espec-1 syntax of the Z39.50
specification. In fact, the internal representation of an element set
specification is identical to the Espec-1 structure, and we'll refer
you to the description of that structure for most of the detailed
semantics of the directives below.
NOTE: Not all of the Espec-1 functionality has been implemented yet.
The fields that are mentioned below all work as expected, unless
otherwise is noted.
The directives available in the element set file are as follows:
defaultVariantSetId OID-name
If variants are used in the following, this should provide the
name of the variantset used (it's not currently possible to
specify a different set in the individual variant request). In
almost all cases (certainly all profiles known to us), the name
Variant-1 should be given here.
defaultVariantRequest variant-request
This directive provides a default variant request for use when
the individual element requests (see below) do not contain a
variant request. Variant requests consist of a blank-separated
list of variant components. A variant compont is a comma-
separated, parenthesized triple of variant class, type, and
value (the two former values being represented as integers). The
value can currently only be entered as a string (this will
change to depend on the definition of the variant in question).
The special value (@) is interpreted as a null value, however.
simpleElement path ['variant' variant-request]
This corresponds to a simple element request in Espec-1. The
path consists of a sequence of tag-selectors, where each of
these can consist of either:
o A simple tag, consisting of a comma-separated type-value pair in
parenthesis, possibly followed by a colon (:) followed by an
occurrences-specification (see below). The tag-value can be a
number or a string. If the first character is an apostrophe ('),
this forces the value to be interpreted as a string, even if it
appears to be numerical.
o A WildThing, represented as a question mark (?), possibly
followed by a colon (:) followed by an occurrences specification
(see below).
o A WildPath, represented as an asterisk (*). Note that the last
element of the path should not be a wildPath (wildpaths don't
work in this version).
The occurrences-specification can be either the string all, the
string last, or an explicit value-range. The value-range is
represented as an integer (the starting point), possibly
followed by a plus (+) and a second integer (the number of
elements, default being one).
The variant-request has the same syntax as the
defaultVariantRequest above. Note that it may sometimes be
useful to give an empty variant request, simlply to disable the
default for a specific set of fields (we aren't certain if this
is proper Espec-1, but it works in this implementation).
The following is an example of an element specification belonging to
the GILS profile.
simpleelement (1,10)
simpleelement (1,12)
simpleelement (2,1)
simpleelement (1,14)
simpleelement (4,1)
simpleelement (4,52)
4.6. The Schema Mapping (.map) Files
Sometimes, the client might want to receive a database record in a
schema that differs from the native schema of the record. For
instance, a client might only know how to process WAIS records, while
the database record is represented in a more specific schema, such as
GILS. In this module, a mapping of data to one of the MARC formats is
also thought of as a schema mapping (mapping the elements of the
record into fields consistent with the given MARC specification, prior
to actually converting the data to the ISO2709). This use of the
object identifier for USMARC as a schema identifier represents an
overloading of the OID which might not be entirely proper. However, it
represents the dual role of schema and record syntax which is assumed
by the MARC family in Z39.50.
NOTE: The schema-mapping functions are so far limited to a
straightforward mapping of elements. This should be extended with
mechanisms for conversions of the element contents, and conditional
mappings of elements based on the record contents.
These are the directives of the schema mapping file format:
targetName name
A symbolic name for the target schema of the table. Useful
mostly for diagnostic purposes.
targetRef OID-name
An OID name for the target schema. This is used, for instance,
by a server receiving a request to present a record in a
different schema from the native one. The name, again, is found
in the oid module of YAZ.
map element-name target-path
(repeatable) Adds an element mapping rule to the table.
4.7. The MARC (ISO2709) Representation (.mar) Files
This file provides rules for representing a record in the ISO2709
format. The rules pertain mostly to the values of the constant-length
header of the record.
NOTE: This will be described better.
5. The Input (Data) File Format
The retrieval module is designed to manage data derived from a variety
of different input sources. When used on the client side, the source
format may be GRS-1 ISO2709. On the server side, the source may be a
structured ASCII file, augmented by a set of patterns that describe
the structure of the document.
What we think of as the native source format - the one that is
guaranteed to provide complete access to the facilities of the module,
is an "SGML-like" syntax, based on an inferred DTD, which is in turn
based on the profile information from the various files mentioned in
this document.
Like SGML, an input record consists of tags and data. The tags are
enclosed by brackets (<...>). As a general rule, each tag should be
matched by a corresponding close tag, identified by the same tag name
preceded by a slash (/).
6. License
Copyright (C) 1995-2000, Index Data.
This is the Index Data "P" license - it applies exclusively to the
record management module of the YAZ system, and to this document.
Permission to use, copy, modify, distribute, and sell this software
and its documentation, in whole or in part, for any purpose, is hereby
granted, provided that:
1. This copyright and permission notice appear in all copies of the
software and its documentation. Notices of copyright or attribution
which appear at the beginning of any file must remain unchanged.
2. The names of Index Data or the individual authors may not be used
to endorse or promote products derived from this software without
specific prior written permission.
THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT WARRANTY OF ANY KIND,
EXPRESS, IMPLIED, OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. IN
NO EVENT SHALL INDEX DATA BE LIABLE FOR ANY SPECIAL, INCIDENTAL,
INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER OR NOT
ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF LIABILITY,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
SOFTWARE.
7. About Index Data
Index Data is a consulting and software-development enterprise that
specialises in library and information management systems. Our
interests and expertise span a broad range of related fields, and one
of our primary, long-term objectives is the development of a powerful
information management system with open network interfaces and
hypermedia capabilities.
We make this software available free of charge, on a fairly
unrestrictive license; as a service to the networking community, and
to further the development of quality software for open network
communication.
We'll be happy to answer questions about the software, and about
ourselves in general.
Index Data Ryesgade 3 DK-2200 Copenhagen N
Phone: +45 3536 3672
Fax : +45 3536 0449
Email: info@indexdata.dk