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IVOA Interop, Cambridge UK, 20071 IVOA Data Access Layer Table Access Protocol Analysis Doug Tody (NRAO/NVO ) I NTERNATIONAL V IRTUAL O BSERVATORY A LLIANCE.

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Presentation on theme: "IVOA Interop, Cambridge UK, 20071 IVOA Data Access Layer Table Access Protocol Analysis Doug Tody (NRAO/NVO ) I NTERNATIONAL V IRTUAL O BSERVATORY A LLIANCE."— Presentation transcript:

1 IVOA Interop, Cambridge UK, IVOA Data Access Layer Table Access Protocol Analysis Doug Tody (NRAO/NVO ) I NTERNATIONAL V IRTUAL O BSERVATORY A LLIANCE

2 IVOA Interop, Cambridge UK, TAP Context Architecture –Cross-match portal/application –Table Access Protocol –ADQL specification –VOSpace, UWS, SSO, etc. Role of TAP –Direct access to table data at a single site –Support for higher level distributed queries –Broader future role in DAL (complex data etc.)

3 IVOA Interop, Cambridge UK, Primary TAP Use-Cases Complex/Large Table Query –Large query (async, vospace, authentication) –Multi-table operations (join etc.) –Multi-region queries (table upload) –Advanced ADQL/SQL capabilities Required to support cross-match portal, advanced apps Full functionality is required Simple Table Query –Filter-type operation upon a single table –Most basic astronomical catalog access is of this type –ADQL, async useful but not required for simple queries Probably sufficient for most small data providers Cone search is not enough

4 IVOA Interop, Cambridge UK, Primary TAP Use-Cases Table Metadata Query –Metadata describing stored data is also data –can be virtual, subsetted, transformed, etc. –Client application queries TAP service for available data –tables, table columns, relationships, etc. –service metadata (capabilities etc) is a separate issue Basic metadata model should be simple Extensibility required for advanced query support Data Access Query –This is "ADQL integration into DAL" –ADQL query against a DAL data model (complex data etc.)

5 IVOA Interop, Cambridge UK, Key Requirements/Issues ADQL and Grid capabilities –Motivation Required for portals and advanced applications Needs ADQL, multi-region, async, vospace, sso, etc. –Issues or Options Not controversial: everyone agrees we need this Not required however for basic usage Complex; will take time to prototype, specify, standardize Unrealistic to expect community implementation w/o frameworks

6 IVOA Interop, Cambridge UK, Key Requirements/Issues Simple Query capability –Motivation Provide simple basic table access capability Needed anyway for simple table metadata queries Adequate for most simple filter-type queries of single table Supplants cone search; much more powerful but still simple Provide robust implementation while we develop advanced stuff –Issues or Options Some want to make ADQL mandatory –"all data should be at data centers" Options: legacy cone search plus ADQL-TAP –but cone search is too limited

7 IVOA Interop, Cambridge UK, Key Requirements/Issues TAP Information Schema –Motivation Provide uniform access to both table data and metadata Same query/access interface used for both Supports virtual data, dynamic queries, format options, etc Easily extended without changing interface Don't do one thing now, another later –Issues or Options Need to specify/agree upon minimal core metadata Strategy: Adopt registry table model with minor changes Other options: VOTable with no data, literal registry XML

8 IVOA Interop, Cambridge UK, Key Requirements/Issues Proposed Core TAP/Registry Table Schema –Table name[[catalog.]schema.]table typebase table, view, output, etc. descriptiontable description –Column namecolumn name tableNametable name descriptioncolumn description unitunit in VO standard format ucdUCD if any utypeUTYPE if any dataTypedataType as in VOTable/registry arrayShapearray "shape"/size as in VOTable/registry stdstandard column (else custom addition)

9 IVOA Interop, Cambridge UK, 20079

10 10 TAP Design Study History –Based upon work done by ESAC/VOQL-TEG and DAL WG in spring 2007 –Also NVO tiger team, SkyNode experience, data center experience TAP Design Goals –Provide capability for ADQL queries to support advanced analysis –Define minimal implementation for small data provider, common queries replace legacy cone search with more general facility –Both data access and metadata access supported natively by service –Provide for scalability, in particular multi-position queries –Support Grid capabilities, i.e, async, staging, authentication –TAP should be consistent with other DAL interfaces where possible –Provide registry integration for automated service discovery

11 IVOA Interop, Cambridge UK, TAP Interface Summary Form of interface –HTTP GET/POST based (other protocols possible, e.g. SOAP, CEA) –Multiple output formats (VOTable, CSV/TSV, XML, VOSpace, etc.) Operations –AdqlQueryADQL-based queries, full functionality –SimpleQuerySimple data queries, metadata queries –GetCapabilitiesReturn metadata describing the service –GetAvailabilityMonitor runtime service function and health

12 IVOA Interop, Cambridge UK, AdqlQuery Operation Scope and Form of Interface –General capability for ADQL-based queries –Both GET and POST versions are required GET is synchronous, indempotent, simple, RESTful POST required for async, staging, large queries –Semantics, e.g., parameters, identical for both versions –ADQL query is URL-encoded so use in GET is not a problem Parameters –QUERYThe query string (ADQL; URL-encoded) –FORMATOutput data format (VOTable, CSV, XML, etc.) – Only used in POST version; for VOSpace – Only used in POST version; for driving UWS –MAXRECMaximum records in the output table –RUNIDPass-through; used for logging (others TBD)

13 IVOA Interop, Cambridge UK, AdqlQuery Operation Field Names, UTYPE and UCD –Suggest this be done at level of field rather than by operation –Literal field names directly access database table –A UTYPE reference resolves into a literal table field name e.g., ssa:Target.Name resolves to table field TargetName –UTYPE (in this context) is a special case of UTYPE ("ucd:") Field name resolution –Both literal and UTYPE/UCD field names resolve to table field –All queries evaluated equivalently after field name resolution –Data models, at the level of TAP, involve only mappings –UFI can automate this, or it can be done client side

14 IVOA Interop, Cambridge UK, AdqlQuery Operation Multi-Position Queries –AKA multi-cone search; but doesn't have to be limited to position –Common use-case involves user source list with thousands of positions –Required for scalability to reduce operation overhead How It Works –Uses ADQL, REGION, POST form of operation –VOTable used to upload source table (ID, POS, SIZE, etc.) other fields are passed through to output output is tagged by source ID can be generalized to any input parameter, not just position –POST (e.g., multipart/form-data) used to upload params, VOTable –Parameters are common to both GET and POST forms Data Scoping –Query, Local (DBMS), and VOSpace (Net) tables are equivalent –POST is a Query space table

15 IVOA Interop, Cambridge UK, SimpleQuery Operation Scope and Form of Interface –Provides capability for simple non-ADQL queries –Used for both data queries and metadata queries (like ADQL/SQL) –Only a synchronous GET version is required –Only a single table is queried at a time Motivation –Simple to implement, easy to use –>90% of actual catalog queries are simple filters of a single table –We need something like this anyway for simple metadata queries but why limit it to only metadata? –Small data providers publish a few simple catalogs –Simpler to implement, likely to be more robust implementation

16 IVOA Interop, Cambridge UK, SimpleQuery Operation Parameters –SELECTTable fields to be returned (default all) –FROMThe table (or view) to be accessed –WHEREA filter to be applied to the table (default none) –POS,SIZEFind data only in this spatial region –FORMATOutput data format –MAXRECMaximum records out –RUNIDPass-through for logging (etc) Provides –Simplified SQL-lite query (90/10 rule) –Both data and metadata queries –Simple cone search capability

17 IVOA Interop, Cambridge UK, SimpleQuery Operation Metadata Queries –Information Schema concept great concept; definition/implementation imperfect but it is a standard, widely (but not completely) implemented –Concept represent database/table metadata as data tables (views) allows use of standard data table interface to query metadata easily extensible without changing service interface views can be used for things such as registry view –Examples FROM=SCHEMA.tables FROM=SCHEMA.columns&WHERE=tableName,foo FROM=SCHEMA.columns&WHERE=tableName,foo&FORMAT=xml

18 IVOA Interop, Cambridge UK, Simple Cone Search Approach –Integrate into SimpleQuery to allow additional constraints would probably be too ambitious in a separate SCS standard –Re-use common DAL position syntax (POS, SIZE) extensible in terms of region type and spatial frame –UTYPE/UCD field syntax allows data models to be used –Table to be queried is specified with FROM –ADQL,REGION provides an advanced alternative with common semantics Examples –REQUEST=SimpleQuery&FROM=foo&POS=180.0,12.5&SIZE=0.2 –REQUEST=SimpleQuery&FROM=foo&POS=180.0,12.5&SIZE=0.2&WHERE=flux,5/

19 IVOA Interop, Cambridge UK, Minimal TAP Service Requirements –Implements SimpleQuery operation possibly getCapabilities and getAvailability as well? –Provides basic data query capability –Provides basic metadata query capability (tables, columns) –No ADQL support required (but may use SQL back end) –No UTYPE support required


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