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    GIS - Lecture 5 GIS - Lecture 5 Document Transcript

    • Attribute Data Models GIS Database Management System GE517 Engr. Ablao Introduction GIS involves both spatial and attribute data. Spatial – geometry of map features Attribute – characteristics of the map features Attribute data are normally stored in tables. Record or tuple – row Field or item – column Attribute intersection of row and column A ib – i i f d l Data models relate spatial & attribute data. GE 517 Geographic Information System 8/20/2010 1
    • Spatial data (left) are linked to attribute data (right) by the label ID. GE 517 Geographic Information System 8/20/2010 File Structures (File-based datasets) Simple list Simplest file structure Unordered/unstructured Arrangement is by whichever comes first Ordered sequential files Simple lists that are arranged according to some order (ex. Alphabetical order) Indexed files An index to the directory is needed for more efficient searches involving finding entries given certain criteria Can be developed as direct files or inverted files GE 517 Geographic Information System 8/20/2010 2
    • Indexed Files Direct Indexed Files Records are used to provide access to other p pertinent information Indirect Indexed Files Index is based on possible search criteria, not on the entities themselves Attributes are the primary search criteria and the entities rely on them for selection GE 517 Geographic Information System 8/20/2010 Flat file database Contains all data in a large file Software could only operate on one file at a time y p Format is very inflexible with respect to the modification of the database structure GE 517 Geographic Information System 8/20/2010 3
    • Flat file database GE 517 Geographic Information System 8/20/2010 Database An integrated set of data on a particular subject Collection of interrelated data stored together with controlled redundancy to serve one or more applications in an optimal fashion Requires more elaborate structure called a database structure or database management system • A DBMS manage attribute data in separate tables GE 517 Geographic Information System 8/20/2010 4
    • Significance of Database Most GIS activities consist of storing entity and attribute data so that we can retrieve any combination of these objects. y j Each graphical feature must be stored explicitly with its attributes so that their combined search becomes faster. GE 517 Geographic Information System 8/20/2010 Advantages of Database over File-based datasets Collecting data at a single location reduces redundancy and duplication p Lower maintenance cost due to better organization and decreased data duplication Multiple applications can use the same data and can evolve separately over time GE 517 Geographic Information System 8/20/2010 5
    • Advantages of Database over File-based datasets User knowledge can be transferred between applications more easily because database remains constant Facilitated data sharing, with a corporate view provided to data managers and users Security and standards for data and data access can be established and enforced GE 517 Geographic Information System 8/20/2010 Types of Database Structure 1. Hierarchical Data Structures 2. Network Systems y 3. Relational Database Structures GE 517 Geographic Information System 8/20/2010 6
    • Hierarchical Data Structure ‘one-to-many’ or ‘parent-child’ relationship Implies that each element has a direct relationship to a number of p p symbolic children Each child is capable of having the same direct relationship with his/her own offspring, and so on. GE 517 Geographic Information System 8/20/2010 Hierarchical database GE 517 Geographic Information System 8/20/2010 7
    • Hierarchical Data Structure Advantages: Simple and straightforward data access since parent and p g p children are directly linked Easy to search since structure is well defined Relatively easy to expand by adding new branches and formulating new decision rules GE 517 Geographic Information System 8/20/2010 Hierarchical Data Structure Disadvantages: Confined to queries along one branch only q g y Difficult restructuring to allow other possible search criteria Creates large index files Redundant entries for searching GE 517 Geographic Information System 8/20/2010 8
    • Network Systems ‘many-to-many’ relationship Each individual data is linked directly to anywhere in the d b using pointers, without the parent- h database h h child relationship. GE 517 Geographic Information System 8/20/2010 Network database GE 517 Geographic Information System 8/20/2010 9
    • Network Systems GE 517 Geographic Information System 8/20/2010 Network Systems Advantages: Less rigid compared to hierarchical structure g p Can handle many-to-many relationships Allows much greater flexibility Reduced redundancy of data GE 517 Geographic Information System 8/20/2010 10
    • Network Systems Disadvantages: In very complex GIS, the number of pointers can become large, th requiring a l t of storage space b l thus ii lot f t Linkages between data must still be explicitly defined using pointers Numerous possible linkages can become extremely tangled, resulting to confusion and incorrect linkages g Not recommended for novice users GE 517 Geographic Information System 8/20/2010 Relational Database Management Systems (RDBMS) Data are stored as ordered records or rows of attribute values called tuples Tuples are grouped with corresponding data rows in a form called relations Each column represents data for a single attribute for the entire dataset GE 517 Geographic Information System 8/20/2010 11
    • Relational Database Management Systems (RDBMS) A key represents one or more attributes whose values can uniquely identify a record in a table. A k common to two tables can establish key bl bli h connection between records in the tables. Primary key – a column which is used to define the search strategy or criterion Foreign key – column in the second table to which the primary key is linked GE 517 Geographic Information System 8/20/2010 Relational database GE 517 Geographic Information System 8/20/2010 12
    • Relational Database Management Systems (RDBMS) Advantages: Allow us to collect data in reasonably simple tables, keeping y p p g organization also simple Capable of doing relational joins, as long as there is at least one column common to the tables to be joined Allows greatest flexibility, both in design and querying GE 517 Geographic Information System 8/20/2010 Normalization of relational database Normalization is a process of decomposition, taking a table with all the attribute data and breaking it down to small tables while maintaining the necessary linkages between them. Normalization is designed to avoid redundant data in tables, to ensure that attribute data in separate tables can be maintained and updated separately and can be linked when necessary, and to facilitate a distributed database database. Normalization slows down data access. GE 517 Geographic Information System 8/20/2010 13
    • PIN Owner Address Sale date Hectares Zone code Zoning P101 Gloria 101 01-20-2001 1.2 1 Residential Pampanga St. Erap 202 San Juan St. P102 Fidel 303 06-30-1992 1.5 2 Commercial Pangasinan St. Cory 404 Tarlac St. P103 Ferdie F di 505 06-30-1965 06 30 1965 2.1 21 2 Commerciall C i Ilocos Norte St. P104 Dado 606 06-30-1961 0.8 1 Residential Pampanga St. Unnormalized table GE 517 Geographic Information System 8/20/2010 PIN Owner Address Sale date Hectares Zone code Zoning P101 Gloria 101 01-20-2001 1.2 1 Residential Pampanga St. P101 Erap 202 01-20-2001 1.2 1 Residential San Juan St. P102 Fidel 303 06-30-1992 1.5 2 Commercial Pangasinan St. P102 Cory 404 06-30-1992 1.5 2 Commercial Tarlac St. P103 Ferdie F di 505 06-30-1965 06 30 1965 2.1 21 2 Commerciall C i Ilocos Norte St. P104 Dado 606 06-30-1961 0.8 1 Residential Pampanga St. First Normal Form GE 517 Geographic Information System 8/20/2010 14
    • Second Normal Form GE 517 Geographic Information 8/20/2010 System Normalized Form GE 517 Geographic Information 8/20/2010 System 15
    • Data Storage in a DBMS Object classes/layers are stored in database tables Each layer is stored as a single database table in a database management system Rows contain objects, while columns contain attributes/properties of the objects GE 517 Geographic Information System 8/20/2010 Basic Database Functions/Operations Join Tables are joined together using common row/column values or keys j g g y After joining two or more tables, a new table is created which contains all the values of the joined tables Database tables can be joined together to create new relations, or views of the database. GE 517 Geographic Information System 8/20/2010 16
    • Basic Database Functions/Operations Link Tables are linked using common row/column values or keys g y Unlike in joining, linking tables does not result to a new table. The original tables are retained but accessing one enables the user to also access a table linked to it GE 517 Geographic Information System 8/20/2010 Database Design Involves three stages: conceptual, logical, and physical Involves six practical steps ( Figure) p p (see g ) GE 517 Geographic Information System 8/20/2010 17
    • Stages of Database Design Conceptual Model Logical Model User View Physical Model Geographic Database Object Types and Database Relationships p Schema Geographic Database Structure Geographic Representation GE 517 Geographic Information System 8/20/2010 Conceptual Model Steps involved are: 1. Model the user’s view Identifying organizational functions, determining data requirements of these functions, organizing data into groups for data management May be presented using a report with tables GE 517 Geographic Information System 8/20/2010 18
    • Conceptual Model 2. Define objects and their relationships Specification of object types/classes and functions, and their p yp relationships May be presented using diagrams GE 517 Geographic Information System 8/20/2010 GE 517 Geographic Information System 8/20/2010 19
    • Conceptual Model 3. Select geographic representation Choosing between the types of discrete objects (point, line, or polygon) or field to represent the data Selection has a critical impact on the database use Although it is possible to switch between representations later on, it would be computationally expensive and would lead to information loss GE 517 Geographic Information System 8/20/2010 Logical Model Steps involved are: 1. Match to geographic database types Matching of object types to be studied to specific data types supported by the GIS 2. Organize geographic database structure Defining topological associations, specifying rules and relationships, and assigning coordinate systems GE 517 Geographic Information System 8/20/2010 20
    • Physical Model Step involved is: Define database schema definition of the actual physical database schema that will hold the database data values usually created using the DBMS software’s data definition language (ex. SQL) GE 517 Geographic Information System 8/20/2010 Attribute data entry Field definition Attribute data entry y Attribute data verification Creation of new attribute data GE 517 Geographic Information System 8/20/2010 21
    • Field definition Definition of (a) field name, (b) data type, (c) data width, and (d) number of decimal places. Data type may be (a) numeric (integer or floating-point), (b) string, (c) Boolean, or (d) date. Consider measurement scale of data. GE 517 Geographic Information System 8/20/2010 Attribute data entry Akin to digitizing for spatial data entry Attribute data need to be entered by typing Given: map with 2,000 polygons and 10 fields Time: At 10 seconds per value, it takes 55 hours – 33 minutes – 20 seconds (2.3 days) to enter 20,000 values Best to determine if an organization has attribute data in digital format (e g NSO) (e.g. GE 517 Geographic Information System 8/20/2010 22
    • Attribute data verification In this step: Ensure attribute data are properly linked to spatial data Verify the accuracy of attribute data May be difficult due to observation errors, out-of-date data, and data entry errors To check for errors: Table may be printed for manual verification y p Computer programs may be written to automate task GE 517 Geographic Information System 8/20/2010 Creation of new attribute data Attribute data classification Example: Elevation High = {Higher than 600 meters} Medium = {Between 200 and 600 meters} Low = {Lower than 200 meters” Attribute data computation Example: Soil erosion potential = rainfall parameter × Soil parameter × topographic parameter × land cover parameter × management parameter Example: Agricultural harvest = area × potential yield GE 517 Geographic Information System 8/20/2010 23