Creating and Maintaining Geographic Databases

Outline Definitions Characteristics of DBMS Types of database Relational model SQL Spatial databases

Definitions Database – an integrated set of data (attributes) on a particular subject Geographic (=spatial) database - database containing geographic data of a particular subject for a particular area Database Management System (DBMS) – software to create, maintain and access databases

A GIS can answer the question: What is where? WHAT: Characteristics of attributes or features. WHERE: In geographic space.

A GIS links attributes to spatial data Attribute Data Flat File Relations Map Data Point File Line File Area File Topology Theme

Flat File RecordValue Attribute RecordValue RecordValue

Advantages of Databases over Files Avoids redundancy and duplication Reduces data maintenance costs Applications are separated from the data –Applications persist over time –Support multiple concurrent applications Better data sharing Security and standards can be defined and enforced

Disadvantages of Databases over Files Expense Complexity Performance – especially complex data types Integration with other systems can be difficult

Types of DBMS Model Hierarchical Network Relational - RDBMS Object-oriented - OODBMS Object-relational - ORDBMS

Historically, databases were structured hierarchically in flat files...

Relational Databases rule now

Characteristics of DBMS Data model support for multiple data types –e.g MS Access: Text, Memo, Number, Date/Time, Currency, AutoNumber, Yes/No, OLE Object, Hyperlink, Lookup Wizard Load data from files, databases and other applications Index for rapid retrieval

Characteristics of DBMS Query language – SQL Security – controlled access to data –Multi-level groups Controlled update using a transaction manager Backup and recovery

Characteristics of DBMS Applications –Forms builder –Reportwriter –Internet Application Server –CASE tools Programmable API

Geographic Information System Database Management System Data load Editing Visualization Mapping Analysis Storage Indexing Security Query Data System Task Role of DBMS

Relational DBMS Data stored as tuples (tup-el), conceptualized as tables Table – data about a class of objects –Two-dimensional list (array) –Rows = objects –Columns = object states (properties, attributes)

Table Row = object Vector feature Column = attribute

Relational DBMS Most popular type of DBMS –Over 95% of data in DBMS is in RDBMS Commercial systems –IBM DB2 –Informix –Microsoft Access –Microsoft SQL Server –Oracle –Sybase

Relational Join Fundamental query operation Occurs because –Data created/maintained by different users, but integration needed for queries Table joins use common keys (column values) Table (attribute) join concept has been extended to geographic case

Relational Databases

SQL Structured (Standard) Query Language – (pronounced SEQUEL) Developed by IBM in 1970s Now de facto and de jure standard for accessing relational databases Three types of usage –Stand alone queries –High level programming –Embedded in other applications

Types of SQL Statements Data Definition Language (DDL) –Create, alter and delete data –CREATE TABLE, CREATE INDEX Data Manipulation Language (DML) –Retrieve and manipulate data –SELECT, UPDATE, DELETE, INSERT Data Control Languages (DCL) –Control security of data –GRANT, CREATE USER, DROP USER

Spatial Search: Gateway to Spatial Analysis Overlay is a spatial retrieval operation that is equivalent to an attribute join. Buffering is a spatial retrieval around points, lines, or areas based on distance.

Image courtesy of K. Foote/M. Lynch, UT-Austin Overlay

Overlay like an attribute join

Types of overlay operations Union Intersect Identity Max Min Etc.

Union computes the geometric intersection of two polygon coverages. All polygons from both coverages will be split at their intersections and preserved in the output coverage.

Intersect computes the geometric intersection of two coverages. Only those features in the area common to both coverages will be preserved in the output coverage.

Identity computes the geometric intersection of two coverages. All features of the input coverage, as well as those features of the identity coverage that overlap the input coverage, are preserved in the output coverage.

Buffer

Complex Retrieval: Map Algebra Combinations of spatial and attribute queries can build some complex and powerful GIS operations, such as weighting. Weighted overlay analysis really just complex retrieval.

Map Algebra Combined with