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Accessing the changing role of database technology within Geographical information Science over the last twenty years, brings to mind the history of GIS ,database management and how the evolving changes in database technology has affected GIS vastly. GIS requires large storage of data, and database management system is used in GIS to facilitate the retrieval and storage of large data collection, includes the protection of data, consistency and the availability of the data whenever it is needed.
GIS deals with the real world not an abstract model, and are applied in a wide range of activities such as defence, environmental management, land management, conservation exploration, emergency services and planning.
Cowen D.J. stated that GIS in relations to database is defined as a system which uses a spatial database to provide answers to the queries of a geographical nature. (1988, pp. 1551). GIS technology provides for the rapid integration of data from a wide variety of sources, with the added benefit of computer graphics assisted display.
Database approach is rooted in an attitude of sharing valued data resources, releasing control of the resources to a multiple user and co-operating in the maintenance of those shared data resources.
Database management system is a computer based system to manage a database or a collection of databases and files. The main function of (DBMS) are database definition, database creation, retrieval(query and reporting), update, programming user facilities for the system development, database revision and restructuring, database integrity control and finally performance monitoring. Database provides a common repository for data so it could be shared by the entire organisation.
Database management systems (DBMS) play a vital role in GIS, because database liberates the GIS field from structuring and maintaining an extensive and complex part of a large software system. (Frank 1988a)
Historical GIS can be traced to historical maps. Historical map repeatedly hold information retained by no other written source, such as boundaries, physical features and name of places that have been redeveloped or modified by modern development. The historical maps have a great deal to offer GIS, which in turn brings new techniques to the analysis and display of the existing maps. Mapping programme developed out of the military necessities for territorial defence after the World War 1, which promoted commercial users adequately getting involved in the discipline.
History of Database Technology
1950s and early 1960s: Magnetic tapes were developed for data storage, processing of data consisted of reading data from one or more tapes and writing data to new tapes. Tapes were read sequentially only and data size was much larger than main memory. This made data processing programs to process data in a particular order by reading and merging data from tapes and card decks.
Late 1960s: The use of hard disk was widely spreading in the late 1960s, changing the scenario for data processing greatly, since hard disk allows direct access to data. With the invention of disk, network and hierarchical database could be created, it also allowed data structure to be stored on disk.
1970s: Codd define the relational model and non procedural ways of querying data in the relational models, it simplicity and possibility of hiding implementation details completely were appealing.
1980s: Relational models were not used in practice initially, due to its perceived performance disadvantages. The relational models could not match the performance of existing network and hierarchical database, which changed with the introduction of system R at IBM research. By the early 1980s, relational database had become competitive with the network and hierarchical database models with regards to its area of performance. The relational database models became easy to use and eventually replaced the earlier database models, which reigned supreme among data models. It allowed much research on parallel and distributed database.
1990s: The SQL language was designed primarily for decision support applications which are query intensive, the use of object-oriented database was also widely spread. The major events were the explosive growth of the World Wide Web, and it made both the relational database and object-oriented database more extensive than latter years.
2000s: The 1st half of the 2000s saw the introduction of XML and the associated query language X query as a new database technology. The recent period have seen a significant growth in the use of open-source database systems mostly MY SQL.
The GIS data requirements are the basic set of design that will dictate the functionality of the GIS application. Users' requirements are translated into a database design for graphic features, tabular attribute data, data relationship that supports the system functionality desired.
Database presentation and formats
Data structure/ relationship
Data acceptance criteria
Presentation and format
Graphic placement standards
Symbol/line/font graphical specification
Data conversion specification
GIS database contain the appropriate data, all of the records have to be reconciled, compiled and interpreted to attain sufficient information to create a meaningful GIS database.
Hierarchical data model
This is one of the oldest database models dating back to late 1950s; the model organizes data in a tree arrangement. There is a chain of command between parent and child data segments. This arrangement implies that a record can have repeating sequence, generally in the child data segments. Data are in series of records, which have a set of field values attached. The hierarchy record types are the equivalent of tables in the relational model, and with the individual records being the equivalent of rows.
Network data model
The popularity of the network data model coincided with the fame of the hierarchical data model. Some data were more naturally modelled with more than one parent per child. The network model permitted the modelling of many-to-many relationships in data.
Relational database model (RDBMS)
It was first developed in the early 1970s, which was slowly adopted by user because of the difficulties associated with converting system implemented with hierarchical and network database management system. Relational DBMS now account for the vast majority of DBMS currently in use. RDBMS is a two dimensional data structure of distinct columns and rows. Its features include persistence, queries, backup and recovery, and transactions.
Properties of Relational Tables
Values Are Atomic
Each Row is Unique
Column Values Are of the Same Kind
The Sequence of Columns is Insignificant
The Sequence of Rows is Insignificant
Each Column Has a Unique Name
Object-oriented database model (OODB)
The model came into existence in the mid to late 1980's. OODB uses object classes and instance and its features are encapsulation, inheritance, object identity, polymorphism and collection.
OODBMS vs. RDMS
Object exit independently, not just as rows in a table
An object is uniquely identified by its OID
An object may have a reference to another object (allowing navigation)
Instead of a table, there are collections, which contain references to object.
A table may be defined as a collection of objects, where every row in the table corresponds to an object.
A row may have a direct reference to another row (allowing navigation)
A row can be used as an object and uniquely identified by its OID
An object may have a reference to another row object (allowing navigation)
Object-Relational database (ORDBMS)
This is a type of database common today. ORDBMS attempt to extend relational database systems with the functionality requirement to support a broader class of applications and to provide a bridge between the relational and object-oriented database management. ORDBMS was created to handle new types of data such as audio, video, and image files that relational database were not equipped to handle which was as a result of increase usage of object oriented database.
Advantages of ORDBMS
It allows users to continue using their existing systems, without having to make major changes.
It allows users and programmers to start using object-oriented systems in parallel.
DBMS have advanced into the Internet and Web Age. Stored data is broadly being accessed through a web browser. At present, queries are being generated through Web-accessible forms and answers are being formatted using a mark-up language such as HTML.
Semi structured data model
The order that is normally associated with a schema is contained within the data, which is most often called ``self-describing''. Semi-structured data is naturally modelled in terms of graphs which contain labels which give semantics to its underlying structure.
Other types of data models are: Associate model, Context Model, Entity-Attribute-Value (EAV) data model