Tuesday, September 22, 2015

Basic data structures used in computers

GIS involves storing entity and attribute data in order to retrieve any combination of these objects. In order to perform these operations the data must be stored in the computer as a file structure. Each graphical entity must be stored explicitly along with its attributes. The following are the basic data structures commonly used in computers:

-Simple lists: It is the most basic file structures
Data is placed in the order in which they are entered
New data is placed at the end
Lack of structure makes searching very inefficient
This list is simple, unstructured and unordered

-Ordered sequential files:
The normal search strategy used here is a divide-and-conquer approach
The number of search operations using this strategy is defined as log2(n+1) operations

-Indexed files:
In this file structure, each entity will have several descriptive attributes assigned to it
An index is required to find a particular entity
Indexed files begin with a set of records and item keys
Indexed files can be indexed either as direct files or inverted files
Indexed files can be used to ignore all other records that do not satisfy the search criteria