Bitemporal Map Registrations
ISBN 978-85-88783-11-9
Authors
1Højholt, P.; 2Hansen, L.D.
1ZOOMOUT.COM Email: phojholt@aol.com
2ADABTO Email: lassedonovan@hotmail.com
Abstract
A new system for handling the geographic description of the official boundaries of administrative units in Denmark has been imple-mented. In 2013 the Danish state commissioned a new system for handling the geographic description of the official Danish administrative units. The dataset will become the official authoritative geographical reference dataset for administrative units in Denmark, and in the coming years it will be included in a multitude of administrative processes. The project is part of a major effort in Denmark to improve and rationalize the organization of basic authoritative data and public administration. At present, 10 different types of administrative units are included in the system. Larger types of units are automatically derived from smaller types of units. The authoritative status of the system’s recordings as part of the public administration in Denmark leads to high demands on the system’s ability to reproduce the current as well as former database states. In the light of this it was decided to include bitemporal timestamps in all recordings in the system. One timestamp for valid time showing from when a record represents the official state of an object and one timestamp for transaction time showing when it was recorded. The present system is a full spatio-temporal system and has separate bitemporal timestamps for geometries and attributes. Each object instance spans multiple records each with their own separate timestamp. The bitemporal method used is simple and yet very powerful and can be set up so that it never requires changes to previously entered records. It can record events that have already taken place, events that will become effective at the time of registration, as well as events that will become effective at some time in the future. Events that occur out of sequence is handled seamlessly, as the system has no general requirement for them to occur in sequence. An instance does not contain any information concerning ‘until when’ the recording is or was the official state. By omitting the ‘until when’ information on both time stamps the model achieves its considerable flexibility and ease of operation. The bitemporal method was derived from five essential business case events. Any record in the system is considered to be the result of an event. The model operates on 5 different types of events. The events are: ‘New Object’, ‘Object Changed’, ‘Object Corrected’, ‘Object Discontinued’, and ‘Object Awakened’. The present system takes its analytic starting point in the events that the system must handle, but for every event it is not the change as such that is stored, but rather the new changed state of the object. The production system includes tools for easy navigation and editing of the full bitemporal landscape of the dataset. In order to avoid unmanageable system complexity, it was decided to construct production tools and processes so that maps are only displayed (and edited) for one combination of valid time and transaction time at a time. After editing the user can send the changes to the database with the chosen valid time, whether it is in the past, present or in the future. As of now, the system has been in active operation for half a year. Both the method of bitemporal registration and the accompanying set of tools have been found to work very well. In the operational period all the five different business events have occurred and the system has shown its value by being able to handle them flawlessly.