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 www.geoinformation.net.

Introduction to the relational data model 09/12/2018

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 09/12/2018

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 09/12/2018

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! 09/12/2018

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 09/12/2018

Creation of tables in SQL Tables are built using the CREATE TABLE command 09/12/2018

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“ 09/12/2018

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. 09/12/2018

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 09/12/2018

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 377-387, 1970 09/12/2018