Points to Cover Recap of what we covered so far A concept of database
Database Management System (DBMS) Database data models
Relational database modelObject-oriented approach
Relationship between spatial and attribute data in GIS
Data management operations in ArcGIS
Spatial Data ModelingStage of data modeling in GIS
Available options
Indentifying the spatial features form the real world that are of interest in the context of the research question
Separating real world into layers of feaures
Choosing how to represent the features
PointsLinesPolygons NetworksSurfaces
Choosing an appropriate spatial data model
Raster modelVector model
Selecting an appropriate spatial data structure to store the model within the computer
Basic raster data structureCompacted raster data structureBasic vector data structure Point dictionary structure Topological vector data structure
Concept of Database A GIS can be described as a spatially-
enabled databaseConventional databases store attribute
dataGIS stores both attribute and spatial data
Database is a set of structured data that are related to each other in some wayOrganized filing cabinetPhone bookOn-line database of academic publications
Concept of Database Many of human activities produce data
that is stored and managed in the database environmentOur society is generating tremendous
amounts of data on daily basisData has become a valuable commodityTo realize its value, the data need to be
managed and shared efficiently
Concept of Database One of the approaches to turning data
into information is a databaseDatabase is more than just a container for
storing dataOrganize data into more meaningful and
usable formHave analytical capabilities
Concept of Database The database approach provides the
following benefitsEase of accessing data Prevention of unnecessary duplication of dataData stored independently of the application
for which they are usedSecure controlled access to dataStandards facilitate data exchangeData in the database can be shared by
different users Manual databases versus computer
databasesWhich are more effective and efficient?
Database Management System
A DBMS is a computer program that controls the storage, retrieval and modification of data in a database (Dale and McLaughlin, 1988)Comprises tools that
perform these functionsAllows users to deal
with the data without knowing much about the database itself
Figure 4.4Source: Heywood et al., 2011
Relational Database Data Model
A DBMS manages data that are organized using a database data modelSet of rules about how the objects and
relationships between them should be represented
Number of different data models used for handling attribute data in GIS
Relational data model is most used by GISThe relational data model is based on
concepts proposed by Frank Codd (1970)
Relational Database Data Model Data are organized and stored in a series of
two-dimensional tables, each of which contains records for one type of entity
Each entity has a unique identifier value assigned to itUnique identifiers allow to link (relate) data in
two or more different tablesThis structure makes possible applying queries to
one or more tables
Relational Database Data Model Types of relationships possible between entities
in a relational database
Figure 4.7Source: Heywood et al., 2011
Relational Database Data Model
Querying a relational databaseQueries are built on expressions based on
relational algebra which in turn is based on Boolean logic
SQL, standard query language, has been developed to facilitate the querying of relational databasesAdvantages: completeness, simplicity,
pseudo-English language styleDisadvantages: was not developed to
handle geographical concepts such as ‘near to’, ‘far from’ or connected to
Object-Oriented Database Approach
More realistic approach to representing spatial entities in the database environmentEncapsulation: Object = State + Behaviour
State: set of values of attributes describing a spatial entity
Behaviour: methods of operating on itComposite objectHierarchy of objects
Subclass Superclass
Figure 4.17Source: Heywood et al., 2011
Object-Oriented Database Approach
Allows arranging objects into hierarchies allows differential assignment of behaviours (Inheritance)Behaviour of subclass objects = ‘own’
behaviour + ‘superclass’ behaviour Benefits of the OO approach for GIS
No differentiation between spatial and attribute data
Works better for graphic operations Disadvantage of the OO approach
Represents world as a series of rigidly bounded objects
Still under development
Data management in ArcGIS The primary data storage mechanism in
ArcGIS is the geodatabaseA collection of geographic datasets of various
types held in a common ‘container’ such as a database file or a database application
Based on an object-relational model Relations (tables) function as objects Behavior is supplied through the geodatabase
application logic implemented as a series of system tables
A key geodatabase strategy is to leverage the database management system (DBMS)Extends SQL application to feature geometry
Data management in ArcGIS Geodatabases comprise
Three primary dataset types Feature classes Raster datasets Tables
Database schema: metatables containing information about object behavior and relationships, maintaining data integrity Topologies Networks Subtypes
Source: ArcGIS 10 Help files
*
Data management in ArcGIS Types of geodatabases
File geodatabases Stored as folders in a file system. Each dataset is held as a file that can scale up to
1 TB in size. Personal geodatabases
Datasets are stored within a Microsoft Access data file
Limited in size to 2 GB ArcSDE geodatabases
Stored in a relational database using Oracle, Microsoft SQL Server, IBM DB2, IBM Informix, or PostgreSQL.
Multiuser geodatabases which are unlimited in size
Relationship between data in GIS Raster datasets
Simple raster datasets no separate attribute data table
Rater datasets with attribute tables Within a geodatabase, the raster attribute
table is saved within the raster dataset and hidden from the user
Source: ArcGIS 10 Help files *
Data Management Operations The supported attribute column types
in the geodatabase
Source: ArcGIS 10 Help files
Data Management Operations
QueriesAttribute query
Used to find features based one particular attribute
Locational query Used to find features with locations that meet
certain conditions Works with four types of relationships: near,
adjacent to, intersect, and insideThe result of queries is a set of selected
features