Georelational data model

Add links
Source: Wikipedia, the free encyclopedia.

A georelational data model is a

vector file format during the 1980s and 1990s, including the Esri coverage and Shapefile.[1]

History

The second era in the history of GIS, starting in the mid-1970s, was characterized by the rise of the first general-purpose GIS software programs (rather than the bespoke systems created in the 1960s and early 1970s). Each of these programs also created its own data file structures, primarily focused on finding innovative ways to store the spatial or geometric aspect of the data in the most efficient and error-free way. One example of this was the POLYVRT software and data structure (1973) from the Harvard Laboratory for Computer Graphics and Spatial Analysis, which inspired the Arc/INFO Coverage format.[2]: 105  In experimental GIS software such as ODYSSEY, attribute data was only handled in a rudimentary way. Meanwhile, the relational database was quickly becoming the most promising software for managing non-spatial data, and several nascent GIS software companies chose to adopt it into their systems, especially Esri.

Although there were exceptions such as the object-oriented data models in Smallworld GIS (1989) and Intergraph's experimental TIGRIS, georelational data dominated the GIS industry until the rise of spatial databases in the late 1990s. Most of them are obsolete, although the Shapefile is still in common (if decreasing) use.

Georelational formats

In any

relational database management system
software.

Examples of commonly-used georelational data formats include:

ARC/INFO Coverage (Esri 1981-2005)
The name ARC/INFO literally reflected the georelational design of the software and the coverage format. The ARC model or Coverage was the
RDBMS
software for the attribute data.
MGE (Intergraph 1989-2000)
During the 1980s, Intergraph was an industry leader on workstation
UNIX workstations, Informix being one of the most common.[4]
An ID attached to each object in the design file enabled a relational join to the rows in the attribute table.
Shapefile (Esri 1992–present)
As the GIS industry grew to incorporate more casual users, the inherent complexity of the coverage data structure became a concern. When Esri released
ArcView GIS 2.0 in 1992, it introduced the new shapefile format for vector data. This was a much simpler data model, eliminating features such as topology, but was still a georelational design. A shape-"file" actually consisted of several files, including at the very least a .shp file to store the geometry, and a .dbf file for the attributes, the latter directly adopting the dBase format that was the dominant microcomputer database at the time (despite it being a proprietary trade secret, the .dbf format had been legally reverse-engineered by the xBase community and published). Rather than using a relational join to connect the two files, the shapefile merely uses file order: the first shape matches the first attribute row, and so on.[5]

See also

  • GIS data model

References

  1. ^ Wade, T. and Sommer, S. eds. A to Z GIS
  2. ISBN 978-1-58948-118-3
    .
  3. ISBN 978-0-471-79229-1
    .
  4. ^ Korte, George B. (1994). The GIS Book (3rd ed.). OnWord Press. p. 63.
  5. ^ ESRI (July 1998). "ESRI Shapefile Technical Description" (PDF). Retrieved 2007-07-04. {{cite journal}}: Cite journal requires |journal= (help)
Retrieved from "https://en.wikipedia.org/w/index.php?title=Georelational_data_model&oldid=1218294942"