Database design
- in each organization or project only certain phenomena are important enough to collect and represent in a database
- database design consists of:
- determining how data are used in the organization or application
- identifying the phenomena which need to be recorded
- choosing an appropriate data representation for selected phenomena
- structuring the data so that they can be manipulated and retrieved as required
FIPS 173
= Federal Information Processing Standard for cartographic data
- FIPS was developed to provide a nationally uniform means for exchanging digital cartographic data
- federal contracts are required by law to provide spatial data in this format
- FIPS 173 standarized many spatial database terms for cartographic data
language in this lecture based on FIPS 173
WWW sources of information on FIPS 173
- ftp://sdts.er.usgs.gov/pub/sdts/articles/ascii/overview.doc
- ftp://sdts.er.usgs.gov/pub/sdts/articles/ascii/profiles.doc
Data model (once again)
- a conceptual description of a database defining entity types and associated attributes
- each entity type is represented by specific spatial objects
- the database model is a view of the database which the system can present to the user
- need not be related directly to the way the data are actually stored in the database
- e.g. census zones may be defined as being represented by polygons, but the program may actually represent the polygon as a series of line segments
Steps in database design
1. Conceptual
- software and hardware independent
- describes and defines included entities
- identifies how entities will be represented in the database
- this is the assignment of spatial objects to entities
Conceptual stage
- requires decisions about how real-world dimensionality and relationships will be represented
- these can be based on the processing that will be done on these objects
- e.g. should a building be represented as an area or a point?
- e.g. should highway segments be explicitly linked in the database?
Data dictionary
- is the reference volume containing
- definitions of all entity types to be included in the database
- list of attributes to be associated with each entity type
- identification of the spatial objects used to represent each entity type
2. Logical
- software specific but hardware independent
- is determined by the
- data base management system (DBMS)
- sets out the logical structure of the database elements
Database structures
- Hierarchical
- Network
- Relational
3. Physical
- both hardware and software specific
- requires consideration of how files will be structured for access from the disk
Desirable database characteristics
- contemporaneous - should contain information of the same vintage for all its measured variables
- as detailed as necessary for the intended applications
- positionally accurate
- exactly compatible with other information that may be overlain with it
Desirable database characteristics - cont.
- internally accurate
- portraying the nature of phenomena without error
- requires clear definitions of phenomena that are included
- readily updated on a regular schedule
- accessible to whoever needs it
Issues in database design
- almost all entities of geographic reality have at least 3-dimensional spatial character
- but not all dimensions may be needed
- e.g. highway pavement has a depth,
- but is not as important as the width,
- which is not as important as the length
- representation should be based on types of manipulations that might be undertaken
- map-scale of the source document is important in constraining the level of detail represented in a database
- e.g. on a 1:100,000 map individual houses or fields are not visible
Codd, E. F., 1981. "Data Models in Database Management," ACM SIGMOD Record 11(2):112-114. Explains the nature of data models, their role in constructing databases.
DCDSTF - Digital Cartographic Data Standards Task Force. 1988. "The proposed standard for digital cartographic data," The American Cartographer 15(1). Summary of the major components of the proposed US National Standard.
Healy, R. G., 1991. "Database Management Systems" in Maquire, D., Goodchild, M., and Rhind, D. (Eds.). GIS: Principles and Applications, Wiley, New York. Helpful overview of hierarchical, network, and relational database management systems.
Robinson, A., R. Sale, J. Morrison, and P. Muehrcke, 1984. The Elements of Cartography, (5th ed.), John Wiley and Sons, New York. Useful survey of cartographic terminology and models.
Unwin D., 1981. Introductory Spatial Analysis, Methuen, London. A spatial analysis perspective on spatial data models.
http://dusk.geo.orst.edu/gis/lec04_add.html