facilitate such implementation are presented. Due to the limited scope of this paper, major 
characteristics of OVPF credited to the object-oriented technology will be discussed. 
5.1. TRANSFORMATION OF RELATIONAL DATA TO OBJECT 
FORMAT 
Data encapsulation property of object-oriented technology allows all information of 
an object to be completely contained. Further more with the ability to represent a complex 
object which are those objects that are composed of other objects, the design of the object- 
oriented format of the VPF data has shown to be an improvement over the traditional flat, 
non-hierarchical approach. All complex objects use object pointers compared to the 
concept of foreign keys for relational databases. These pointers are maintained and 
managed by the system which implies three major advantages: (1) each opbject identifier is 
unique, (2) referential integrity is maintained when changes are made during an update, and 
(3) the expensive use of join tables and operations are completely eliminated. 
Referring to the Figure 2, it is clear that the complex object concept allows a design 
that provides all metadata and feature information of each instance of any features. For 
example, in Figure 2, the segment (A) has all the metadata information object; the segment 
(B) has the feature data object including the topological information; and, segment (C) has 
the spatial indexing information for retrievela and query. For a feature, an object would be 
the complex object as depicted in Figure 2. With this as the basis of an object, two 
methods are used to store objects on disk. 
ParcPlace, Inc. has developed the Binary Object Streaming System (BOSS).A 
BOSS format is an optimized import and export facility for storing complex object webs 
on disk (Arctur Benchmark, Christiansen. ParcPlace Systems. Inc.). BOSS format stores 
objects in an internal, platform-portable, binary format. Such a format provides a compact 
storage and faster retrieval. A difficult task of maintaining any “circular-references” (back- 
pointers between objects) are correctly handled within the BOSS format. For a brief 
summary of BOSS format, see (Arctur Benchmark). 
OVPF now has the capability to store VPF data as persistent objects on disk once 
the relational VPF information from the hierarchical directory structure has been imported 
and migrated to the ODBMS. This also uses the same object format as defined but is using 
ObjectStore ODBMS as the ways of managing and maintaining objects. 
5.2. FEATURE UPDATES 
Once again with data encapsulation property of object-orented technology, feature 
updating is very much local to the feature of interest. Since a feature has both spatial and 
non-spatial information, a feature can be accessed and its spatial or non-spatial or both can 
be changed. 
In OVPF, a feature can be updated in terms of its attribute values or its location 
information. When location information is modified, a careful attention is paid to potential 
changes in the topology. When a feature is selected to be deleted, references to all 
primitives of the feature need to be queried. Since each primitive contains a collection of 
features that reference it, deleting a feature requires removal of any references to the 
primitive of the feature by other features. For those other features in the feature collection 
of each primitive that is deleted, new adjacent primitive need to be defined. Similarly, 
when a new feature is added, all primitives that define the new feature need to check for 
any contiguous and adjacent primitives. For more detail, refer to (Chung et. al.. 1995).