M. Egenhofer. Extending SQL for Cartographic Displays. Cartography and Geographic Information Systems, 18, 1991.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to the query language retrieval functionnalities. The architecture presented below is intended to satisfy these requirements. 3 Architecture There are many ways of designing a user interface for GIS databases. We could (i) integrate display and other interactive requests to the query language [EF88, Ege91, Ege94], ii) create an external module specifically devoted to visualisation and interaction with database extracted informations [Voi91] We chose the latter approach in order to build an open interactive system that would be able to access many heterogeneous DBMS (performance is another argument in ....

....are expressed by means of O 2 Sql [BCD89] the object query language of O 2 . We shortly describe below the main features of the GQL spatial database prototype. In our implementation, we follows the now classical relational approach, extended with abstract data types for modelling spatial data [Gut88, ODD89, Ege91]. It provides the user a uniform approach for spatial and non spatial attributes of geographical objects. A single Geometry data type supports any spatial property. For closure under spatial operators, an object of Geometry type is any combination of points, lines and areas. CARTECH [ANT94] or ....

M. Egenhofer. Extending SQL for Cartographic Displays. Cartography and Geographic Information Systems, 18, 1991.

....departure h, arrival h, #transport) Figure 1 The toy database The relation Network corresponds to the first level of abstraction of the relation Transport. It allows the user to see the relation Transport as a logical graph. We adopt the three step definition process of a GIS query defined in [3]: 1) the actual user query specifying the retrieval of data to be displayed; 2) additional queries, called display queries, necessary to separate query results into more detailed sets, each to be displayed in individual format, and (3) the actual display description specifying how to render the ....

....evolution of the scale; 2) The scales may be different (i.e. the surface of the Tahiti island is 1000 km 2 ) 3) The relative orientation may be altered depending on the number of small squares. The management of scale breaking may be: 1) application dependent (i.e. the SET SCALE of [3]) 2) automatically defined depending on the results of the query or (3) user defined. IV.2 Dealing with the ambiguities To prevent part of these ambiguities, two levels of action may be defined: 1) the definition and the manipulation of the spatial representation and (2) the definition of a ....

Egenhofer M.: Extending SQL for Graphical Display, Cartography and Geographic Information System, Vol 18, n°4,

....[7, 15] are applicable to our context. However, temporal languages other than FTL can be used to query MOST databases. Nevertheless, when using any other language, the query processing algorithm will have to be modified to handle dynamic attributes. Another relevant area is spatial databases (see [28, 18, 11, 9, 10, 12, 17]) Work in this area can be used for defining and processing the spatial operators discussed in section 3. Our work is also relevant to uncertainty in databases (see [1, 25] for surveys) However, as far as we know this area has so far addressed complementary issues to the ones in this paper. ....

M. J. Egenhofer. Extending sql for cartographic display. Cartography and Geographic Information Systems, 18(4), 1991.

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