Persistent Feature Identifiers The Essential Model for Features

Figure 2-25 Conceptual Model of the ‘Real World’ modelling process

2.13. Persistent Feature Identifiers

2.13.1. Problem Statement

Managers of complex geographic information systems require capabilities for incremental update, distributed update, copying and partially modifying data. These capabilities require a more careful examination of the issue of feature identity than has previously been achieved. Identity has implementation, logical, syntactic and philosophical aspects. A complete analysis is not attempted here. Some handling of feature identifiers is necessary in order to represent relationships between features. This is discussed in Topic 8 of the Abstract Specification A troublesome issue in the community is the lack of ability to support value-added information in a cost-effective manner [Hair97]. Value added information is an extension of a primary database which needs persistent feature identifiers in order to allow: • additional information to a base dataset is required for a one-off or transient application • a base of information exists but there is a long term need for additional information that has not been captured in the past formation that has not been captured in the past • partnerships are established based on areas of expertise but sharing some common data, e.g. between telecommunications and electricity utility companies • partnerships are established based on areas of expertise but sharing some common data, e.g. between telecommunications and electricity utility companies • incremental updating and incremental publishing • incremental updating and incremental publishing • maintenance of complex or aggregate objects currently using relationships, see Topic 8. • maintenance of complex or aggregate objects currently using relationships, see Topic 8. Natural Language e.g. English Human Experience Formal Languages Mathematics, Logic, Specification L Inter-domain Service Languages Geometric Language Metric Language Geo-Referencing Language Topologic Language etc. Domain- specific Languages generalization specialization C once p tu al Wo rld Real Wo rld The OpenGIS ® Abstract Specification Page 25 Volume 5: Topic 5: Features • Reference to a geographic feature within a repository from outside the repository and perhaps outside any computing system, e.g. as a string of text in a hand-written letter. We also need persistent, immutable feature identifiers in order to support: • Tracking of feature identity during updates and collaborative working • Proper management of versions • Lineages of data transformations The differences between geographic feature identifiers and many other types of persistent identifiers are of scope and scale. A single geospatial data repository may contain hundreds of millions of features. CORBA Persistent Object Identifiers are intended to identify executing software objects in much smaller numbers. Similarly, the IETF Unified Resource Names are designed for smaller numbers of objects. However, the design of IETF URNs may be appropriate for geographic features even if current implementations of identifier resolvers may not be [URNDNS].

2.14. Resolving Scoped Feature Identifiers