Lecture 8. Database Management and Queries

Transcription

1 Lecture 8 Database Management and Queries

2 Lecture 8: Outline I. Database Components II. Database Structures A. Conceptual, Logical, and Physical Components III. Non-Relational Databases A. Flat File B. Hierarchical Databases C. Network Databases IV. Relational Databases A. Hybrid Databases V. Joining and Relating Tables VI. Attribute Queries

3 I. Database Components DBMS (Database Management System): A specialized computer program for organizing and manipulating data. Note: A database is the organized collection of data, often created or manipulated with the help of a DBMS. The terms Database and DBMS should not be used interchangeably.

4 I. Database Components Attributes, Fields, or Items Records, Rows, or N-tuples Entity: A collection of related data items (instances) that are treated as a unit (roads, lakes, etc.) Instance: A specific item of the entity (a specific road, a specific lake)

5 I. Database Components Database Components and Actions DBMS Actions: -Define - Insert - Delete - Query - Update

6 I. Database Components Advantages (Useful Functions): - Prevent redundancy - Increase data quality and data independence - Centralized control - Multiple user views

7 II. Database Structures Database structures define entities and their relationships and specify how tables are connected to one another. 3 Types: Conceptual Physical Logical

8 II. Database Structures Conceptual Component A graphical representation of the entities and relationships in the database. Often represented in a schema

9 II. Database Structures Logical and Physical Components Logical: Refers to the specific database model or type and is defined by the software (i.e., relational, network, etc.). Influences the specific physical structures. Physical: Organization of the data on the computer and the way in which files are linked together.

10 III. Non-Relational Databases Flat Files

11 III. Non-Relational Databases Hierarchical Databases

12 III. Non-Relational Databases Network Databases

13 IV. Relational Databases

14 IV. Relational Databases Hybrid Databases Most often used for GIS data. Attribute data stored in a relational table while coordinate data is stored in a network (or other) structure.

15 V. Joining and Relating Tables One-to-One Relationship Table One-to-Many & Many-to-One Relationship Table GIS Layer GIS Layer

16 V. Joining and Relating Tables Tables are related through Keys. Keys are items or fields that meet certain requirements (data format and length) and are used to index the records. Note: Misspelling or spaces in key values (not field names) can create problems with your join or relate process. Ex. Northridge vs Nothridge or NewMexico vs New Mexico.

17 V. Joining and Relating Tables Joining Tables: Appends the attributes from one table onto another based on a field (key) common to both. Relating Tables: Defines a relationship between two tables - also based on a common field (key) - but doesn't append the attributes of one table to the other. Instead, you can access the related data when necessary.

18 V. Joining and Relating Tables To obtain info about a key field, go to Layer Properties and click on the Fields tab. After joining a table, you can preserve the join by right-clicking on the shapefile or feature class and selecting Data Export Data.

19 VI. Attribute Queries One of the most common functions of a DBMS A selection of a subset of data based on attributes. Can be simple or complex. Boolean Operators: may be applied alone or in combination. AND OR NOT Set Operators: less than: < greater than: > equal to: = Not equal to: < >

20 VI. Attribute Queries AND operator typically decreases selection sets.

21 VI. Attribute Queries OR operations typically increase or add to selections. NOT is a negation operation. i.e. select records that do not equal a specified condition.

22 VI. Attribute Queries SQL (Structured Query Language) Provides the capability to both define and manipulate data. To create SQL queries, go to: Selection Select by Attributes OR Attribute Table Options Select by Attributes

23 VI. Attribute Queries To preserve the result of a query you can: Right click the layer and choose Selection Create Layer from Selected Features (Temporary in the Map Document). Right-click the layer and choose Data Export Data (Permanent Saves to a new shapefile or feature class).