Using The Explain Facility Denis Lynch SilverPlatter Information +44 (181)

Rationale n Many clients don’t know their servers – Users point clients at new servers – Servers add or change databases & services n Clients need dynamic information – Server hours of operation – Billing rates – Supported attribute combinations – Field labels

Explain Database Schema TargetInfoTermListDetailsExt. Svcs. InfoCategoryList Server-wide Information RecordSyntaxInfoSchemaInfoTagSetInfoVariantSetInfo Universal Information DatabaseInfoAttributeDetailsElementSetDetailsRetrievalRecordDet Database-specific Information AttributeSetInfoUnitInfo TermListInfoSortDetailsProcessingInfo

TargetInfo n There is one TargetInfo record per database n Target name and nicknames n IR parameters (esp. database combinations) n Message of the day n Contact and access information n Network addresses

Universal Information Records n A dynamic way to get static information – All keyed by an Object Identifier n TagSetInfo lists all tags defined in a tagset n SchemaInfo lists – Mapping of tagset numbers to tagsets – The record structure n RecordSyntaxInfo describes the record structure n AttributeSetInfo lists every attribute

DatabaseInfo n One DatabaseInfo record per database n Database name n Databases that can be searched with this one n Databases that are subsets of this one n AccessInfo lists OIDs etc. for –Attribute sets, syntaxes, schemas, query types... n Copyright and contact information

AttributeDetails n Lists all attributes supported for this database n May list patterns for legal combinations { { { Use, {4, 16, 24} }, { Structure, All } }, { { Use, 1001 }, { Structure, 2 } } } { { { Use, {4, 16, 24} }, { Structure, All } }, { { Use, 1001 }, { Structure, 2 } } }

Term Lists n One TermListInfo per database, lists “indexes” – An arbitrary name to link to TermListDetails – A title, for display to users – A search cost hint (optimized, expensive…) – A scannable flag n TermListDetails may apply to many databases – Attribute combinations that access this term list – More info about scanning – Sample terms

Retrieval record details n ElementSetDetails for Element Set Names – ESN + Record Syntax will get: – Schema used at the server – Specific elements in the retrieval record n RetrievalRecordDetails for CompSpec – Schema + Record Syntax will get – Mapping of schema elements to record elements

SortDetails n Lists all the sort keys available for database n Lists equivalent element and attribute specs n No provision for server defined “sortfield”

ProcessingInformation n Can convey usage, formatting, semantics... n Application “kinds” distinguish usage n Processing information is EXTERNAL n Syntax OID is part of Brief record

Finally n ExtendedServicesInfo lists supported services – Identified by OID of Package syntax – Availability, cost… – Is package retained in ES database? – Can ES be executed synchronously? n CategoryList lists categories of records – Dynamically discover what can be dynamically discovered

How clients use Explain - Search n Basic characteristics in AccessInfo n TermList titles for access points n Or USE attributes from AttributeCombinations n AssociatedDBs can be searched together n Lots of text for “Describe” function n SubDBs supports “more specific” function

How clients use Explain - Retrieval n Pick ESN from ElementSetDetails n Check for a record syntax you can handle n Use subDBs to understand returned DB names n Use PerElementDetails for field labels n Use ProcessingInformation if you know how

Implementation status n Supported in some toolkits, e.g. yaz n Supported by a few servers, e.g. SilverPlatter –The information is often hard to collect –The incentive is low n Not used by any general clients –“Commercial quality” user interfaces need tailoring –Simpler interfaces rely on Bib-1 and US-MARC –Co-operative systems use tight profiles