1. Geo-Databases: lecture 2 The Relational Data Model
Prof. Dr. Thomas H. Kolbe
Institute for Geodesy and Geoinformation Science
Technische Universität Berlin
Credits: This material is mostly an english translation of the course module no. 8 (‘Geo-Datenbanksysteme‘) of the open e-content platform

2. Introduction to the relational data model
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3. Fundamentals of the relational model
Structure:
All data is presented in tables (relations)
Fixed number of columns (attributes)
Variable number of rows (tuples or datasets)
All values of one column from the same value domain
Characteristrics:
Simple structuring
Set-oriented processing
Avoidance of redundancy by splitting and distribution of data into multiple tables
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4. Operations Projection onto certain columns of a table
With this background, the following operations are particularly useful:
Projection onto certain columns of a table
Selection of certain rows of a table on the basis of a specific selection criterion
Joining data from different tables
Implemented in the query language SQL
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5. Structured Query Language (SQL)
Popular, ISO standardised query language (currently: SQL:2003)
SQL is based on natural language concepts
SQL can be subdivided into the following areas:
Data Definition Language (DDL) for creation and modification of tables
Data Manipulation Language (DML) for updating and querying of data
Due to the complexity we will just give an overview of SQL:1999 (for more information see literature)
For the time being all examples will be based on SQL:1999!
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6. Tables in SQL To begin with: single columns
Each column of a table is assigned exactly one data type
A data type defines the set of possible values and the allowed operations for this type
Important data types:
integer: integer numbers
real: floating-point numbers
numeric(p,s): fixed-point numbers with precision p and scale s
char(L): character string with fixed length L
varchar(L): character string with maximum length L
date: data type for representation of dates
blob(L): Binary Large Object, binary data with maximum length L
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7. Creation of tables in SQL
Tables are built using the CREATE TABLE command
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8. Identification of data sets
Problem: How can we identify tuples unambiguously?
Solution: We need a key that unambiguously identifies each tuple!
A key may comprise multiple attributes.
There can be multiple keys for one table.
Possible keys for the sample table:
“Nr“
“Name“, “Straße“, “Ort“
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9. Primary key It is advantageous to name a primary key to the system:
CREATE TABLE Studenten (… PRIMARY KEY (MatNr) …);
If no suitable primary key can be found, an artifical key may be generated by the system.
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10. Foreign key
Foreign keys in one table always refer to primary keys of other tables
By means of a foreign key we can relate tuples from different tables
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11. References
Overview:
Ramez Elmasri, Shamkant B. Navathe, Fundamentals of Database Systems, 3. Ed., Addison Wesley, 2001
Hector Garcia-Molina, Jeffrey D. Ullman, Database Systems: The Complete Book, Prentice Hall, 2002
Jim Melton, Alan R. Simon, SQL 1999: Understanding Relational Language Components, Morgan Kaufmann Publishers, 2001
Seminal work:
E. F. Codd, A relational model of data for large shared data banks, in: Communications of the ACM, Vol. 13, Seite , 1970
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