Geographical Information Systems

Geog 481/506                                                                                                  Tu Th 3:30-4:50pm
Fall 2011                                                                                                          Fillmore 170

Instructor: Ling Bian                                                                                          LabA: Tue:   5-6:20pm, W145, Chunyuan diao
Office: 120 Wilkeson                                                                                        LabB: Thur:  6:30-7:50pm, W145, Tong Sun
Office hours: Tu Th 2-3pm  or by appt.                                                             LabC: Fri:  10-11:20am, W145, Tong Sun

Databases

1. GIS databases

    A database is a shared collection of data with secure controlled access
    Data are stored independently of their applications.
 
    A GIS database contains geographic data

    A DBMS is a collection of software programs that facilitates the efficient and effective
    storage and access of data

    A GIS DBMS

 

2. Levels of data abstraction

    Conceptual data model - user's perception of the real world
    Logical data model - a formal description of the data model
    Physical data model - physical storage of the data (e.g., format, order, path)

 

3. Database functions
    Records, fields, and keys
    Map librarian and tiles
 
    Adding, updating and deleting records
    Extracting information from data
    Maintaining data security and integrity
    Supporting applications

4. Database data models (logical data models)
   (1) Hierarchical data model
    Data records are organized by the hierarchy of a key field. It allows one parent and multiple children
            Root
            Parent
            Children
 
    Advantages:
            Easy to understand
            Easy to update
            Fast to retrieve information due to the direct link

    Disadvantages:
        A search is only based on the key field
        One must know the hierarchy structure before the search
        No multiple parents are allowed,  leading to redundant data

(2) Network data model

        It allows multiple parents and children with no root
 
        Pointer - a code that indicates a location in a file

    Advantages:
        No data redundancy

    Disadvantages:
        The linkage information costs storage space
        It is difficult to update

(3) Relational data model

         The database consists of several two dimensional tables.
         A row is a record and a column is a field.    

      Characteristics

         Every field can be used as a key in a search 
         A cross file search can be done by join, as long as at least one filed is common to both files
         A link table can be created with needed attributes without actually taking storage space

    Advantages:
      Flexible, no structure restrictions for search
      Easy to understand
      Less data redundancy

    Disadvantages:
      It can be time consuming to search matching values

   (4) Object-oriented data model
        Objects

     Attributes
     Operations

    Inheritance
      Data and functions are organized in a hierarchy
      Objects inherit characteristics and functions of their ancestor objects

    Encapsulation
      Data and functions are combined in one object

    Association and aggregation

    Advantages and disadvantages
      Easy for modeling and the representation is close to human perception
      Reduce the complexity of software development

    Disadvantages:
      Current systems are a hybrid of relational and object-based databases

    Object-relational databases
        uses an enriched set of graphic element types on top of
        the three basic types of points, lines, and polygons.

 

5. Reading: Chpt 3.