Array DBMS: Difference between revisions

Revision as of 21:58, 18 September 2014

Revision as of 07:01, 19 September 2014

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A first declarative query language suitable for multiple dimensions and with an algebra-based semantics has been published by [[Peter Baumann (computer scientist)|Baumann]], together with a scalable architecture.<ref>Baumann, P.: [http://www.informatik.uni-trier.de/~ley/db/journals/vldb/vldb3.html#Baumann94 On the Management of Multidimensional Discrete Data]. VLDB Journal 4(3)1994, Special Issue on Spatial Database Systems, pp. 401 - 444</ref><ref>Baumann, P.: [http://www.informatik.uni-trier.de/~ley/db/conf/ngits/ngits99.html#Baumann99 A Database Array Algebra for Spatio-Temporal Data and Beyond]. Proc. NGITS’99, LNCS 1649, Springer 1999, pp.76-93</ref> Another array database language, constrained to 2-D, has been presented by Marathe and Salem.<ref>Marathe, A., Salem, K.: A language for manipulating arrays. Proc. VLDB’97, Athens, Greece, August 1997, pages 46 - 55</ref> Seminal theoretical work has been accomplished by Libkin et al.;<ref>Libkin, L., Machlin, R., Wong, L.: A query language for multidimensional arrays: design, implementation and optimization techniques. Proc. ACM SIGMOD’96, Montreal, Canada, pp. 228 - 239</ref> in their model, called NCRA, they extend a nested relational calculus with multidimensional arrays; among the results are important contributions on array query complexity analysis. A map algebra, suitable for 2-D and 3-D spatial raster data, has been published by Mennis et al.<ref>Mennis, J., Viger, R., Tomlin, C.D.: Cubic Map Algebra Functions for Spatio-Temporal Analysis. Cartography and Geographic Information Science 32(1)2005, pp. 17 - 32</ref>

In terms of Array DBMS implementations, the [[rasdaman]] system has the longest implementation track record of n-D arrays with full query support. [[Oracle Spatial|Oracle GeoRaster]] offers chunked storage of 2-D raster maps, albeit without SQL integration. [[TerraLib]] is an open-source GIS software that extends object-relational DBMS technology to handle spatio-temporal data types; while main focus is on vector data, there is also some support for rasters. Starting with version 2.0, [[Postgis|PostGIS]] embeds raster support for 2-D rasters; a special function offers declarative raster query functionality. [[SciQL]] is an array query language being added to the [[MonetDB]] DBMS. [[Michael_StonebrakerMichael Stonebraker#SciDB|SciDB]] is a more recent initiative to establish array database support. Like SciQL, arrays are seen as an equivalent to tables, rather than a new attribute type as in rasdaman and PostGIS.

For the special case of [[Sparse matrix|sparse data]], [[OLAP]] data cubes are well established; they store cell values together with their ___location - an adequate compression technique in face of the few locations carrying valid information at all - and operate with SQL on them. As this technique does not scale in density, standard databases are not used today for dense data, like satellite images, where most cells carry meaningful information; rather, proprietary ad-hoc implementations prevail in scientific data management and similar situations. Hence, this is where Array DBMSs can make a particular contribution.

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Formally, an array ''A'' is given by a (total or partial) function ''A'': ''X'' → ''V'' where ''X'', the ''___domain'' is a ''d''-dimensional integer interval for some ''d''>0 and ''V'', called ''range'', is some (non-empty) value set; in set notation, this can be rewritten as { (''p'',''v'') | ''p'' in ''X'', ''v'' in ''V'' }.

Each (''p'',''v'') in ''A'' denotes an array element or ''cell'', and following common notation we write ''A''[''p''] = ''v''.

Examples for ''X'' include {0..767} × {0..1023} (for [[Xga#Extended_Graphics_ArrayExtended Graphics Array|XGA]] sized images), examples for ''V'' include {0..255} for 8-bit greyscale images and {0..255} × {0..255} × {0..255} for standard [[RGB]] imagery.

Following established database practice, an array query language should be [[Declarative programming|declarative]] and safe in evaluation.

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A declarative geo raster query language, [[Web Coverage Processing Service]] (WCPS), has been standardized by the [[Open Geospatial Consortium]] (OGC).

In June 2014, ISO/IEC JTC1 SC32 WG3, which maintains the SQL database standard, has decided to add multi-dimensional array support to SQL as a new column type,<ref>Chirgwin, R.: [http://www.theregister.co.uk/2014/06/26/sql_to_worlddog_we_doing_big_data_too/|SQL fights back against NoSQL's big data cred with SQL/MDA spec], [http://www.theregister.co.uk|The Register]], 26 Jun 2014</ref>, based on the initial array support available since the [[SQL:2003|2003 version of SQL]]. The new standard will be named ''ISO 9075 Part 15: Multi-Dimensional Arrays (SQL/MDA)''.

== List of Array DBMS ==