Research on Realizing Spatial-temporal Database Based on Historical Relational Database
Cui Weihong · National Remote Sensing Bulletin · 2008
Spatial-temporal database researches on how to store historical and current spatial-temporal data so as to track and analyze changes of some region,which finally implements spatial-temporal modeling and geographical simulation process.At present there are mainly two solutions as for spatio-temporal database.The one is adding time dimension on the basis of spatial database.The other is extending spatial dimension on the basis of temporal database.The research on spatial database has already been mature at the present time.So we should fully make use of existing spatial data model and spatial processing and analyzing functions of GIS,which will reduce enormously workload.Consequently this paper chooses to add time dimension on the basis of spatial database.Extended relational spatio-temporal database extends time dimension by considering time as attribute of spatial geometry and thematic feature,which has its particular advantages.For one thing,relational database is supported by strict relational algebra and has many available large commercial relational databases.In addition,many information systems are originally established on the basis of relational database.In the second place many researches on temporal database itself mostly adopt relational model,which extend temporal semantics for relational algebra and develop temporal structured query language.Thirdly many researches on spatial database in GIS domain also employ relational data model,and research on spatial query language is also based on relational model.All in all,spatial-temporal database adopting model of historical relational database can make the best of research results and existing systems such as temporal query function of temporal relational database and spatial process and analysis function of GIS,reducing the cost of establishing spatial-temporal database.This paper at first introduces historical relational database model,temporal relational algebra and temporal query language,and then conducts researches on historical relational database to organize temporal information in spatial database.Aiming at completely relational spatial database,this paper makes use of temporally upward compatible function of ATSQL2 and adopts the mode of transplanting non-temporal database to temporal database to extend temporal information for spatial data.In the light of organizing principle of spatio-temporal data,current data and historical data are stored separately.As a result,spatio-temporal database includes current spatial database and historical spatial database.Current database stores the latest base state version of map layers,yet historical database stores historical base state version of map layers.If spatial data and attribute data change,data of new version will be added to current spatial database.At the same time original data will become data of old version and be shifted to historical spatial database.We can adopt indexing pointer to establish the relationship between current spatial database and historical spatial database.The paper eventually gives an example of rotating wheat fields to examine the feasibility and validity of adopting model of historical relational database to establish spatial-temporal database.Rotating wheat fields has obvious temporal trait.Generally speaking,it is not likely that wheat fields change in aspect of spatial geometry.Most changes of wheat fields are changes of attributes such as plant type and owner.When plant type of a wheat field changes,it is considered that the old geographic entity disappears,and a new one comes into being.We need to add a new record in the current database and transfer the original record to the historical database.In the mean time we adopt PreVersion and PostVersion to record successive relationship between them.The result shows that spatial-temporal database based on historical relational model is feasible and valid.However,spatio-temporal database based on historical relational database still has the shortcomings.In addition,it can not deal with transaction time yet,at which database objects are created,updated and deleted.Consequently in future work we should take disposal ability of transaction time to spatio-temporal database into account.