This technical area contains an overview of the architecture along with a set of documents.

• Technical guides - give detailed technical information on each component of DNF.
• Other documents - contains other supporting technical papers.
• Terminology - gives definitions and examples of the specialist terms commonly used within the DNF documentation

Introduction to the
Architecture of DNF

Basic Concepts

Much data is related to locations on the earth’s surface. These locations are usually specific geographic or spatial objects in the real world (e.g. buildings, land parcels, streets). Applications, which are designed to process and analyse data which needs to be spatially referenced, model a particular view of the world. The geographic objects are abstracted and represented in the application in many different ways. Spatial aspects are often represented by geometric primitives such as points, lines, and areas.

Position is related to a spatial referencing system such as the National Grid or latitude and longitude. The properties of the objects are reflected in attribute values. Other data is also usually included such as identifier, date of capture, date of last change and so on. These basic concepts are shown in a much simplified form in Figure 2. The “business objects” shown in the diagram can be to any real world objects that need to be located; they are not restricted to those associated with human activity.

Figure 2: Abstraction and representation of geographic and business objects in an application for processing geographic information

The geometrical aspects and position of geographic objects is often derived in some way from a reference base, traditionally this has been some sort of topographic map such as OS Land-Line. Increasingly this is from sources which use object-based models of the real-world such as OS MasterMap which is rich in maintained and uniquely identified topographic objects (See Figure 3).

Figure 3: Abstraction and representation of geographic objects using a reference base

This opens up the possibility of creating and maintaining permanent associations between the geographic objects used in the application (application reference objects) and objects in the reference base (base reference objects). The advantages in doing this can be manifold:

• it may be possible to relate the business objects directly to the geographic objects present in the reference base thus obviating the need to maintain separate geographic objects in the application;
• changes to geographic objects reflected in changes to the reference base can be used to update those geographic objects modelled in the application;
• deriving and then maintaining the geometry of the geographic objects represented in the application from a reliable, accurate and maintained reference base can lead to greater consistency and improved data integrity in the application;
• by maintaining an association with a reference base which is also used by other applications a means is provided of associating the geographic objects from different applications;
• by maintaining an association with a common reference base and doing this in a consistent way, according to agreed practice, opens up the possibility of data sharing and interoperability.

These latter concepts are shown below in Figure 4.

Figure 4: Simplified diagram showing how applications can be associated with a reference base to enable cross-referencing

The nature of the association between the application reference objects and the base reference objects making up a common reference base will depend on a number of factors:

• the closeness in views of the real world between the application reference objects and reference base – how similar or how dissimilar is the abstraction in terms of real world objects included or excluded;
• the similarity of the abstraction in terms of attribution and geometric representation (e.g. as points, lines and areas) - this is about their degree of semantic similarity as well as their spatial “footprint”;
• the classification of the application objects into different types ~ the granularity in terms of spatial detail and attribution between the application objects and the reference base;
• the life-cycles and maintenance regimes of the application objects and the objects making up the reference base.

There is unlikely to be a complete geometrical, temporal and semantic “fit” between the application reference objects and the base reference objects, therefore any association has to be qualified in some way through the additional or ancillary geometry and other attribution applied to the association itself. The concepts described above are core to DNF

In essence DNF is about how you can associate geographic objects used in different applications to a common reference base and, by so doing, provide a means of relating different business objects used in the applications where they are referenced to the same, or a very similar, location. As more applications use this approach so the range of business objects that can be cross-referenced increases.