Download Geographic Databases - GIS and Mapping - Lecture Notes and more Study notes Geology in PDF only on Docsity!
Chapter 10 Creating and Maintaining Geographic Databases (^) 131
Creating and Maintaining
Geographic Databases
OVERVIEW
After people, the database is arguably the most important part of a GIS because of the costs of collection and maintenance, and because the database forms the basis of all queries, analysis, and decision making. Today, virtually all large GIS implementations store data in a database management system (DBMS), a specialist piece of software designed to handle multi-user access to an integrated set of data. Databases need to be designed with great care, and to be structured and indexed to provide efficient query and transaction performance. A comprehensive security and transactional access model is necessary to ensure that multiple users can access the database at the same time. On-going maintenance is also an essential, but very resource-intensive, activity.
LEARNING OBJECTIVES
By the end of this chapter students should: Understand the role of database management systems in GIS; Recognize structured query language (SQL) statements; Understand the key geographic database data types and functions; Be familiar with the stages of geographic database design; Understand the key techniques for structuring geographic information, specifically creating topology and indexing; Understand the issues associated with multi-user editing and versioning.
Chapter 10 Creating and Maintaining Geographic Databases (^) 132
KEY WORDS AND CONCEPTS
DBMS, (RDBMS, ODBMS, ORDBMS), parsers, middleware, object classes, database tables, keys, normal forms, SQL, SQL/MM, database design, indexes, B-tree indexes, grid indexes, quadtree indexes, R-tree indexes, database editing and update, transactions, long transactions, versioning
OVERVIEW
10.1 Introduction 10.2 Database management systems 10.3 Storing data in DBMS tables 10.4 SQL 10.5 Geographic database types and functions 10.6 Geographic database design 10.7 Structuring geographic information 10.8 Editing and data maintenance 10.9 Multi-user editing of continuous databases 10.10 Conclusion
CHAPTER SUMMARY
10.1 Introduction
A database can be thought of as an integrated set of data on a particular subject. Geographic databases are simply databases containing geographic data for a particular area and subject. Lists the advantages of the database approach to storing geographic data over traditional file-based datasets including reducing redundancy, decreasing costs, allowing multiple applications, transfer of knowledge, data sharing, security and standards, concurrent users Disadvantages include cost, complexity, single user performance decreased Describes how to create and maintain geographic databases, and the concepts, tools, and techniques that are available to manage geographic data in databases.
10.2 Database management systems
A DBMS is a software application designed to organize the efficient and effective storage and access of data.
Chapter 10 Creating and Maintaining Geographic Databases (^) 134
10.3 Storing data in DBMS tables
The lowest level of user interaction with a geographic database is usually the object class (also called a layer or feature class), which is an 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. o Rows contain objects ( instances of object classes) o Columns contain object properties or attributes The data stored at individual row, column intersections are usually referred to as values. Geographic database tables are distinguished from non-geographic tables by the presence of a geometry column (often called the shape column). To save space and improve performance, the actual coordinate values may be stored in a highly compressed binary form. Tables are joined together using common row/column values or keys. Following joins, all tables can be treated as a single table Lists Codd‘s five principles for the efficient and effective design of tables and introduces the concept of normal forms Normal forms improve the simplicity and stability of a database and reduce redundancy of tables by splitting them into sub-tables that are re-joined at query time Notes that large tables common in geographic applications leads to tendency for non-normalized table designs in GIS Includes a worked example of normalization of a simple land parcel tax assessment table
10.4 SQL
The standard database query language adopted by virtually all mainstream databases is SQL (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 The third major revision of SQL (SQL 3) which came out in 2004 defines spatial types and functions as part of a multi-media extension called SQL/MM. There are three key types of SQL statements: DDL (data definition language) used to create, alter and delete relational database structures
