Geodatabase Database Design. Tomislav Sapic GIS Technologist Faculty of Natural Resources Management Lakehead University

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1 Geodatabase Database Design Tomislav Sapic GIS Technologist Faculty of Natural Resources Management Lakehead University

2 Table Design Two types of attribute tables in GIS: Feature attribute table Non-spatial attribute table Table fields are variables and attributes in the fields are values. (Although in some non- GIS database descriptions, fields/columns are referred to as attributes). When designing a table and its fields and attributes the overall rules are: Simple attributes Attributes of minimal length Individual attributes smallest element Attributes are easily understandable and searchable Attributes are unambiguous Potential for errors is minimized Data redundancy is reduced Potential logical inconsistency is avoided

3 Database Design In order to reduce the overall data size and redundancy a database is often separated into smaller tables that are related and linked to each other, creating a relational database. The process of redesigning tables to reduce data redundancy and potential logical inconsistency, including, when needed, creating separate tables linked to each other, is called normalization. Database normalization is defined through degrees of normalization First Normal Form, Second Normal Form, Third Normal Form, Fourth Normal Form, Fifth Normal Form, etc. A common GIS database conforms to the Third Normal Form and those below it. The goal of the normalization: Avoid redundant data and waste space that may cause data integrity problems. Avoid possible logical inconsistency. To ensure the separate tables can be maintained and updated separately and linked when necessary. To facilitate a distributed database (Cheng 2006) The normalization of databases was first proposed and explained by E.F. Codd, an IBM researcher, in his 1970 paper A Relational Model of Data for Large Shared Data Banks (Codd 1970). Since then, the whole concept has been somewhat modified but the main components of it are still valid.

4 Database Normalization Un-normalized table (multiple, redundant values) First Normal Form (1NF) First Normal Form (1NF) Source: Chang (2006) 1. There s no top-to-bottom ordering to the rows. 2. There s no left-to-right ordering to the columns. 3. There are no duplicated rows (there is a (composite) Primary Key field in the table). 4. Every row-and-field intersection contains exactly one value for the applicable domain (and nothing else).

5 Second Normal Form (2NF) The table should conform to 1NF. All non-prime attributes should be functionally dependent on a primary key (or the whole of a composite primary key). A Primary Key is a field with unique values, that identifies each record in the table. A Foreign Key is a field with non-unique values and which individual values match values in a Primary Key field. A Foreign Key field is used to connect a table to another table with a Primary Key field and can contain non-unique values. Another and widely used definition of 2NF is that a non-prime field cannot be dependent on a subset of a composite primary key. Second Normal Form (2NF) Source: Chang (2006)

6 Third Normal Form (3NF) The table should conform to 2NF. All non-prime fields can be functionally dependent only on a primary key field and not on a non-prime field. The above type of functional dependency between non-prime fields can potentially cause logical inconsistency in the data (data quality!). Primary Key Foreign Key Third Normal Form (3NF) Source: Chang (2006)

7 Database Design - Table Join in ArcGIS Often, related data are stored in two or more different tables for the reasons of database simplification, easier editing and management, smaller size. Two tables can be joined as long as they both have a field in which some or all values are the same as in the field in the other table(s) and the values are stored as the same data type. The linking field in the origin table is called the primary key and in the destination table the foreign key. There are three types of relationships between two tables: o One to One o One to Many o Many to Many Origin Table Destination Table Primary Key ArcGIS 10.1, Help Destination Table Foreign Key Many to Many ons.com/developer- Tips/Tip/May- 2011/Many-to-Many- relationships-in-the- Kentico-CMS-Cont.aspx One to Many Origin Table ArcGIS 10.1, Help Origin Table Destination Table Destination Table

8 Database Design In ArcGIS, origin vs destination table and simple vs composite relationship. Primary key Foreign key

9 Database Design In ArcGIS, it is important to get the origin and destination table right.

10 Sources: Chang, Kang-tsung Introduction to Geographic Information Systems. McGraw Hill Higher Education. Third Edition. Codd, E.F A relational model of data for large shared data banks. Communications of the ACM, Vol Kent, W A Simple Guide to Five Normal Forms in Relational Database Theory. Communications of the ACM, Vol 26(2).