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Translating WFS Query to SQL/XML Query

Translating WFS Query to SQL/XML Query. Vânia Vidal Fernando Lemos Fábio Feitosa Departamento de Computação Universidade Federal do Ceará. Outline. WFS Specification Contributions Feature Type Specification Extension of Feature Type Translating WFS Query to SQL/XML Query Conclusions.

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Translating WFS Query to SQL/XML Query

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  1. Translating WFS Query to SQL/XML Query Vânia Vidal Fernando Lemos Fábio Feitosa Departamento de Computação Universidade Federal do Ceará

  2. Outline • WFS Specification • Contributions • Feature Type Specification • Extension of Feature Type • Translating WFS Query to SQL/XML Query • Conclusions

  3. WFS Specification • OpenGis Consortium • promotes the development and use of advanced open system standards and techniques in the geoprocessing area and related information technologies • WFS • publishes GML views of geographic features stored in data sources • users can query and update data stores through a feature type schema

  4. WFS Specification • WFS request • GetCapabilities • DescribeFeatureType • GetFeature • Transaction • LockFeature

  5. Contributions • Correspondence Assertions • specify the mappings between feature type schemas and relational schemas • TranslateWFSQuery Algorithm • translates a WFS query over a feature type schema into a SQL/XML query over the relational schema • translation is based on the correspondence assertions

  6. WFS GetFeature Request Deegree WFS SQL Query Q1 WFS Query … BDR Deegree WFS Server SQL Query Qn GML result of Q1 … result of Qn Our approach WFS Query SQL/XML Query BDR GML Publisher WFS Server GML GML

  7. Feature Type Specification • Feature Type F over a relational schema S F = <T, R, A> where T is the XML Schema type for feature instances R is the name of the master relation schema,which contains the geometric attribute A is the set of correspondence assertions, which fully specifies T in terms of R

  8. Example Relational Schema DB_Station XML Schema type for Feature Type F_Station Master Relation Schema

  9. Correspondence Assertions of F_Station Master Relation Schema

  10. Extension of a Feature Type • Extensionof F = <T, R, A> for an instance sof schema S • a sequence of F-elements of type T, such that each F-element matches a tuple of s(R) F = { $f | $f is an instance of T and rs(R) such that $fAr} • SQL/XML query definition of an extension of F F = SELECT XMLELEMENT( "Extension_of_F ", XMLAGG( XMLELEMENT( "F", [RT](r) )) FROM Rr [RT](r) constructs the content for an instance $f of T such that $f A r as specified by the CAs of F

  11. SQL/XML Definition for Extension of F_Station [TStation / code]  [Station_rel / CODE] SELECT XMLELEMENT( "Extension_of_F_Station", XMLAGG( XMLELEMENT( "F_Station", XMLFOREST(S.CODE AS "code"), XMLFOREST( SDO_UTIL.TO_GMLGEOMETRY(S.GEOM_POINT) AS "geometry"), XMLFOREST(S.NAME AS "name"), XMLELEMENT( "address", XMLFOREST(S.STREET AS "street"), XMLELEMENT( "city", (SELECT XMLCONCAT( XMLFOREST(C.NAME AS "name"), XMLFOREST(C.AREA AS "area")) FROM City_rel C WHERE C.CODECITY = S.CODECITY) ), XMLFOREST(S.ZIPCODE AS "zipcode") ), (SELECT XMLAGG(XMLELEMENT( "pluviometry", XMLFOREST(PL.MONTH AS "month"), XMLFOREST(PL.VALUE AS "value") ) ) FROM Pluviometry_rel PL WHERE S.CODE = PL.CODESTATION), XMLFOREST( (SELECT A.NAME FROM Agency_rel A WHERE A.CODEAGENCY = S.CODEAGENCY) AS "agency") ) ) ) FROM Station_rel S; [TStation / geometry]  [Station_rel / GEOM_POINT] [TStation / name]  [Station_rel / NAME] [TStation / address]  [Station_rel / NULL] [TAddress / street]  [Station_rel / STREET] [TAddress / city]  [Station_rel / FK1] [TCity / name]  [City_rel / NAME] [TCity / area]  [City_rel / AREA] [TAddress / zipcode]  [Station_rel / ZIPCODE] [TStation / pluviometry]  [Station_rel / FK2-1] [TPluviometry / month]  [Pluviometry_rel / MONTH] [TPluviometry / area]  [Pluviometry_rel / AREA] [TStation / agency]  [Station_rel / FK3 / NAME]

  12. An Instance of DB_Station

  13. Extension of F_Station

  14. Extension of F_Station

  15. Extension of F_Station

  16. Extension of F_Station

  17. WFS Query • <Query> element of a GetFeature request: • delivers feature instances of a given feature type, where each feature instance matches a tuple of the Master Table • <Query> element contains: • a mandatory attribute typeName • used to indicate the name of the feature type to be queried • a sequence of zero or more <wfs:PropertyName> elements • used to specify what properties to retrieve • the value of each <wfs:PropertyName> element is an XPath expression that references a property or sub-property of the relevant feature type • an optional <Filter> element • used to define spatial and non-spatial constraints on a query • encoded as described in the OGC Filter Encoding Implementation Spec

  18. QX : Canonical XQuery for QW QW : WFS Query over F_Station The result of Qw is the result of evaluating QX on an extension of F_Station

  19. XML fragment resulting from QW QW : WFS Query

  20. WFS Query Definition: Let QW be a WFS Query over feature type F Qxbe the canonical XQuery for QW QS be a SQL/XML query over S which returns a set of <gml:featureMember> elements. Then, we say that QSis a correct translation forQW iff, for any instance S of S, if F is the extension of F on S S1 is the set of <gml:featureMember> elements resulting from evaluating QS on S and S2 is the set of <gml:featureMember> elements resulting from evaluating QX on F then S1 =S2

  21. TranslateWFSQuery Algorithm Input: WFS query QW Output: SQL/XML query QS Let <P,L > := TranslateFilter( f ), where f is the filter of QW In case of Case 1: QW has no <wfs:PropertyName> elementsQs = SELECT XMLELEMENT( "gml:featureMember", XMLELEMENT( "F",[RT][r] ) ) FROM Rr, L WHERE P

  22. TranslateWFSQuery Algorithm Case 2:QW has n<wfs:PropertyName> elements Let Pathi be the value of i-th <wfs:PropertyName> element of QW. Let Qi [r] := TranslatePath(Pathi) Qs = SELECT XMLELEMENT( " gml:featureMember ", XMLELEMENT( " F ",Q1 [r] … Qn [r] ) ) FROM Rr, L WHERE P

  23. TranslateWFSQuery Algorithm • TranslateFilter( f ) returns a tuple <P,L> where Pis an SQL conditional expression L is a list of relations names required to process P such that, for any instance $t of T if $tAr, where r is a tuple of R, then $t satisfies f iff r satisfies P

  24. TranslatePath(F) Algorithm Input: a path F = p1 /…/ pn of type T Output: SQL/XML subquery Q[r] that computes the value of path F Theorem: For any instance $t of Extension of F, where $t Ar, then Q[r] returns a set S of pn-elements where S = $t/ p1 /…/ pn

  25. Translation for QW QX : Canonical XQuery for QW QW : WFS Query

  26. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station", Q1[S], .........…..…………………..TranslatePath( name ) Q2[S],……........................TranslatePath( address / city) Q3[S],…………….…………TranslatePath( pluviometry ) Q4[S]…………………………..TranslatePath( geometry )) ) FROM Station_rel S, L WHERE P

  27. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station") XMLFOREST(S.NAME AS "name"), Q2[S], Q3[S], Q4[S]) FROM Station_rel S, L WHERE P TranslatePath( name ) [TStation / name]  [Station_rel / NAME]

  28. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station") XMLFOREST(S.NAME AS "name"), XMLELEMENT( "city", (SELECT XMLCONCAT( XMLFOREST(C.NAME AS "name"), XMLFOREST(C.AREA AS "area") ) FROM City_rel C WHERE C.CODECITY = S.CODECITY)), Q3[S], Q4[S] ) FROM Station_rel S, L WHERE P TranslatePath( address / city ) [TStation / address]  [Station_rel / NULL] + [TAddress / city]  [Station_rel / FK1] + [TCity / name]  [City_rel / NAME] + [TCity / area]  [City_rel / AREA]

  29. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station") XMLFOREST(S.NAME AS "name"), XMLELEMENT( "city", (SELECT XMLCONCAT( XMLFOREST(C.NAME AS "name"), XMLFOREST(C.AREA AS "area") ) FROM City_rel C WHERE C.CODECITY = S.CODECITY)), (SELECT XMLAGG(XMLELEMENT("pluviometry", XMLFOREST(PL.MONTH AS "month"), XMLFOREST(PL.VALUE AS "value") ) ) FROM Pluviometry_rel PL WHERE S.CODE = PL.CODESTATION), Q[ S ] ) FROM Station_rel S, L WHERE P [TStation / pluviometry]  [Station_rel / FK2-1] + [TPluviomety / month]  [Pluviometry_rel / MONTH] + [TPluviomety / value]  [Pluviometry_rel / VALUE] TranslatePath( pluviometry )

  30. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station") XMLFOREST(S.NAME AS "name"), XMLELEMENT( "city", (SELECT XMLCONCAT( XMLFOREST(C.NAME AS "name"), XMLFOREST(C.AREA AS "area") ) FROM City_rel C WHERE C.CODECITY = S.CODECITY)), (SELECT XMLAGG(XMLELEMENT("pluviometry", XMLFOREST(PL.MONTH AS "month"), XMLFOREST(PL.VALUE AS "value") ) ) FROM Pluviometry_rel PL WHERE S.CODE = PL.CODESTATION), XMLFOREST(SDO_UTIL.TO_GMLGEOMETRY(S.GEOM_POINT) AS "geometry") ) FROM Station_rel S, L WHERE P [TStation / geometry]  [Station_rel / GEOM_POINT] TranslatePath( geometry )

  31. Translation for QW SQL/XML Query SELECT XMLELEMENT("gml:FeatureMember", XMLELEMENT("Station") XMLFOREST(S.NAME AS "name"), XMLELEMENT( "city", (SELECT XMLCONCAT( XMLFOREST(C.NAME AS "name"), XMLFOREST(C.AREA AS "area") ) FROM City_rel C WHERE C.CODECITY = S.CODECITY)), (SELECT XMLAGG(XMLELEMENT("pluviometry", XMLFOREST(PL.MONTH AS "month"), XMLFOREST(PL.VALUE AS "value") ) ) FROM Pluviometry_rel PL WHERE S.CODE = PL.CODESTATION), XMLFOREST(SDO_UTIL.TO_GMLGEOMETRY(S.GEOM_POINT) AS "geometry") ) FROM Station_rel S, Agency_rel A WHERE S.CODEAGENCY = A.CODEAGENCY AND A.NAME = 'FUNCEME' AND mdsys.sdo_relate( S.GEOM_POINT, mdsys.sdo_geometry(2003, NULL, NULL, mdsys.sdo_elem_info_array(1, 1003, 3), mdsys.sdo_ordinate_array(-5.2, -42.5, –2.5, -38.7)), 'mask=ANYINTERACT querytype=WINDOW') = 'TRUE' <P,L > := TraslateFilter(f )

  32. TranslateWFSQueryAlgorithm Theorem: Let Qw be a WFS Query over F QX be a canonical XQuery for QW QS be a SQL/XML query over S generated by TranslateWFSQuery S1 be a set of <featureMember> elements resulting from QX on F S2 be a set of <featureMember> elements resulting from QS on S Then S1 = S2

  33. Conclusions • Contributions: • a formalism to specify the mapping between a feature type schema and a relational database schema • an algorithm that translates a WFS query over a feature type schema into a SQL/XML query over the relational database schema,based on feature type's correspondence assertions. • Future work: • development of GML Publisher, a framework for publishing geographic data stored in relational databases as GML

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