1. 9. Creating and Maintaining Geographic Databases

2. Outline Definitions Characteristics of DBMS
Types of database
Geographic Extensions
Storing data in DBMS tables
SQL
Structuring geographic Information
Indexing methods
Conclusions

3. Definitions
Database – an integrated set of data 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.
– Virtually all large GI databases are based on DBMS technology

4. Advantages of Databases over Files
Avoids redundancy and duplication
Reduces data maintenance costs
Applications are separated from the data (allowing multiple applications)
Better data sharing
Security and standards can be defined and enforced
Support multiple concurrent applications

5. Disadvantages of Databases over Files
Complexity
Performance – especially complex data types; singer user performance decreased
Integration with other systems can be difficult

6. Types of DBMS Relational (RDBMS)
A relational database comprises a set of related tables, each a two-dimensional list (or array) of records containing attributes about the objects under study
Object (ODBMS)
ODBMS initially designed to address weaknesses of RDBMS:
inability to store complete objects directly in the database, poor performance for many types of geographic query
Not commercially successful
Object-relational (ORDBMS)
an RDBMS engine with an extensibility framework for handling objects

7. Characteristics of DBMS (1)
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

8. Characteristics of DBMS (2)
Query language – SQL
Security – controlled access to data
Multi-level groups
Controlled update using a transaction manager
Backup and recovery
Applications and APIs
DBA tools
Configuration, tuning

9. Geographic DBMS Extensions
Commercial and Open Source DBMS have spatial database extensions to standard ORDBMS
IBM – DB2 Spatial Extender and Informix Spatial Datablade
Oracle Spatial
Spatial capabilities in the core of Microsoft SQLServer
Open-source DBMS PostgreSQL has also been extended with spatial types and functions (PostGIS).
None is a complete GI software system
Focus is on data storage retrieval and management

10. Role of DBMS

11. Storing Data in DBMS Tables
Object class : organized collection of data on a particular theme
Object classes are stored in a standard database table, a two-dimensional array of rows and columns
Rows contain objects (instances of object classes)
Columns contain object properties or attributes
Tables are joined together using common keys

12. Table Column = property Table = Object Class Row = object
Object Classes with
Geometry called Feature Classes

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

14. 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

17. Relation Rules (Codd, 1970)
Only one value in each cell (intersection of row and column)
All values in a column are about the same subject
Each row is unique
No significance in column sequence
No significance in row sequence

18. (A) raw data ParcelNumb OwnerNam OwnerAddress PostalCode ZoningCode
ZoningType
Date / AssessedValue
673/100
Jeff Peters
10 Railway Cuttings
114390 2
Residential
Joel Campbell
1115 Center Place
Dave Widseler
114391 3
Commercial
452 Diamond Plaza
D Widseler
Sam Camarata
19 Big Bend Bld
Chris Capelli
Hastings Barracks
114392
Sheila Sullivan
10034 Endin Mansions
(A) raw data

19. (B) cleaned data in a GIS DBMS

20. SQL
The standard database query language adopted by virtually all mainstream databases
Structured or Standard Query Language:
ISO Standard ISO/IEC 9075
May be used directly via command line, compiled in a general-purpose programming language or via a GUI
Three key types of SQL statement:
DDL (data definition language) used to create, alter, and delete relational database structures
DML (data manipulation language) used to retrieve and manipulate data
DCL (data control language) handle authorization and access

21. SQL
SELECT parcel.ParcelNO, Owner.Address, parcel.AssessedValue FROM (zoning INNER JOIN parcel ON zoning.ZoningCode = parcel.ZoningCode) INNER JOIN owner ON pardel.OwnerSSN = parcel.OwnerSSN WHERE (((parcel.AssessedValue) >300000) AND ((zoning.ZoningType) = ”Residential”));

22. Indexing
Geographic databases tend to be very large and geographic queries computationally expensive
Indexes speed up searching by allowing random instead of sequential access.
A database index is, conceptually speaking, an ordered list derived from the data in a table.

23. 1-d B-tree (balanced tree)
To find a specific value, such as 72, using the index involves a maximum of six tests: one at level 1, one at level 2, and a sequential read of four records at level 3.
An example B-tree index

24. A multi-level grid geographic database index
2D Indexing
Grid index
A multi-level grid geographic database index

25. Raster Grid quadtree index

26. Summary Database – an integrated set of data on a particular subject
Databases offer many advantages over files
Relational databases dominate
DBMSs are vital part of large modern operational GI systems
They store, access and manipulate geographic data using the SQL query language
DBMS requires a DBA to control database structure and security, and to maximize performance
GI system field has extended standard DBMS to store and manage geographic data and beyond