engleski

Lifestyles - a new Paradigm in Spatio-Temporal Databases

This thesis investigates operations affecting identity of objects in a spatiotemporal database, ubiquitous for future temporal GIS. Two different techniques to record change in databases are compared: database versioning and object versioning. We show formally that these techniques are equivalent and we use conceptually simpler model of database versioning for the further development. The conceptual model of our database is based on the entity-relationship model. The complete temporal database is a series of snapshots, each of which represents the state of the universe of discourse at a particular moment on the time scale. Each snapshot consists of a set of objects connected with relations. Objects are metaphorically perceived as having life: an object has its birth or creation, its life or existence, its death or destruction. The central concept in the life of an object is its identifier, which is unchanged from the birth to the death of an object. Identifiers are system constructs and they are maintained by the database independently of the user. Category theory and many-sorted algebras provide the formal background for this thesis. Executable algebraic specifications are written in a categorical, point-free style of functional programming using Gofer environment. Gofer is a dialect of the functional language Haskell. It supports many-sorted algebras by multi-parameter classes. The major result is the formal model for a universal spatio-temporal database, capable of representing different classes of objects in a uniform way with respect to change in identity of objects. We propose a theory of lifestyles: algebras of operations affecting identity of objects. Lifestyles are compositions of basic operations: create, destroy, suspend, and resume. The mereological relation (is part of) is the most important relationship among objects that affects the existence of composite objects and their parts. The concept of suspending parts when composed into a whole abstracts the detail in hierarchical cognitive reasoning. We stress the differences between two major groups of compositions: fusions (composed parts are destroyed and cannot be resumed) and aggregates (composed parts are suspended and can be resumed). The theory of lifestyles is compared with the work of other authors on the topic of identity change. It is formally shown that our system is capable to represent all operations enumerated in other models, being at the same time conceptually simpler and more flexible. Finally, we apply the theoretical apparatus on several categories of real world objects, ranging from the examples in physical domain (natural objects, movable artifacts, liquids, containers, living beings) to non-tangible objects in the social realm (partnerships, ownership rights, and administrative units). We show that metaphorical mappings between the physical and social domain is possible. The major benefit is the reusability of functions and concepts that can be explored in building interoperable temporal information systems.

object orientation; identity; change; spatiotemporal databases; functional programming; algebraic specifications; metaphorical mapping

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