Deriving Spatial Integrity Constraints from Geographic Application Schemas

Integrity constraints of various kinds must be observed when creating or updating a database in order to preserve the semantics and the quality of stored data (Elmasri & Navathe, 2000). Within the scope of geographic applications, integrity assurance requires special attention from the designer, since most geographic applications use data that depend on spatial relationships (Egenhofer & Franzosa, 1991), thereby requiring the specification of spatial integrity constraints. In the traditional database approach, there is a relationship between conceptual, logical, and physical design, in which, through mapping operations, constraints that are identified in the conceptual schema are inherited and transformed into implicit constraints expressed by the data definition language (DDL) or into explicit constraints coded in the application programs (Elmasri & Navathe, 2000). This relationship also exists in spatial information systems; therefore, spatial constraints can be likewise identified and implemented. However, even though there is a very active research area interested in the design of robust and efficient spatial databases, there are still shortcomings with respect to spatial integrity constraints (Borges, Davis & Laender, 2002; Plumber & Groger, 1997). This happens mostly because a simple geometric modification in a single object in a spatial database may generate the need to check for possible integrity violations throughout many object classes, using computationally intensive geometric and topologic algorithms. Most spatial integrity constraints are, in fact, semantic integrity constraints applied to the spatial representation of objects and to the relationships among object instances that are based on spatial representations. In order to be able to adequately represent such representations and relationships in geographic applications design, tools that are more specific and capable of capturing the semantics of geographic data, offering higher abstraction mechanisms and implementation independence (Borges, Davis & Laender, 2001; Câmara, 1995) are required. From geographic application database schemas, developed using an adequate data model, representations and spatial relationships can be extracted; thus, spatial integrity constraints can be specified. This paper focuses on the types of spatial integrity constraints that derive from spatial data modeling constructs, as a part of spatial databases design. OMT-G (Borges et al., 2001), an object-oriented data model for geographic applications, is used to illustrate the concepts involved in the definition of such constraints.