Cách tiếp cận quản lý phiên bản đòi hỏi phải phù hợp với khái niệm hướng đối tượng. Bảng mô tả các phương pháp tiếp cận chính được phát triển để quản lý các phiên bản trong cơ sở dữ liệu và ứng dụng của họ trong một bối cảnh GIS. | OBJECT-ORIENTED ANALYSIS AND DESIGN 43 VERSION MANAGEMENT APPROACHES According to Loomis Versioning is the tracking of the evolution of an object s state through time 1992 p. 40 . Deciding on a version management approach for a spatiotemporal data model involves finding a way to integrate the approach and the model. The version management approach requires being consistent with object-oriented concepts. Table describes the main approaches developed for managing versions within databases and their application in a GIS context. Currently two main strategies are used to represent multiple versions of an object within an object-oriented database. The first strategy consists of version numbers or time stamps being associated with every attribute or relationship of an object. These attributes or relationships may then be chained giving them a historical order. The result is a single object and identity OID with the versions actually associated with the attributes. This approach could have advantages only in models in which the objects have several attributes as well as changes occurring to only a few attributes. The second strategy is to track versions at the level of objects rather than attributes. Chaining the old object and any older versions to the new version creates a new version of an object. As a result a different identifier OID is associated with the new version hence each version has its unique identifier within the version configuration. So far no performance studies have been undertaken on these alternatives. Nevertheless both alternatives involve the design of operations for handling the dynamic behaviour of versions within the object-oriented data model. Ordering versions within a data model is an important aspect in object orientation. Despite the development of storage devices such as optical disks offering new capabilities for storing large amounts of data a significant waste of storage space will still be minimised by ordering versions .
