Database Technologies. Madalina CROITORU IUT Montpellier

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1 Database Technologies Madalina CROITORU IUT Montpellier

2 Course practicalities 2 x 2h per week (14 weeks) Basics of database theory relational model, relational algebra, SQL and database modelling Modern database theory: NoSQL The course will also benefit from notions presented in the Software Engineering course (this is why the SQL course will be done after the modelling part) Exams: 2 Written exams (relational algebra, SQL) On-going notation projects and homeworks Contact: croitoru@lirmm.fr

3 Reading material This course is based on the following book:

4 Motivation: Storing data? Imagine you have to design a software allowing the management of a flat renting business. These are the requirements: The company has several branches throughout the UK (we need to store their street name, number, city and postcode. Staff (for whom we need to record the name, surname, position, sex, dob and salary) work in one branch at a time. A branch manages several properties for rent. The properties are managed by a staff member and the information regarding the properties are as follows: the street, city, postcode, type, no of rooms, rent and owner details (name, surname, address, phone, ). A client (for whom we store the name, surname, telephone, and renting preferences: type and maximum rent) can view properties. A client is registered by a member of staff upon joining the agency, In the case of a viewing one should record the viewing date and the comment of the client.

5 Your data organisation How would you store this kind of information? (Imagine you have 5 fictional branches, 6 members of staff, 6 properties to rent, 4 clients, 4 private owners and 5 viewings). Imagine different functionalities of software running on this kind of data. What can it do?

7 Your data organisation How would you store this kind of information? (Imagine you have 5 fictional branches, 6 members of staff, 6 properties to rent, 4 clients, 4 private owners and 5 viewings). Question 1: What happens if I want to run the program on my computer using the F:\ drive? How would this impact the applications? Question 2: What happens if one staff members changes their name (gets married)? Question 3: What happens if a client changes their phone number?

8 Part 1 RELATIONAL MODEL

9 Relational Model for DBs Currently the dominating software in use today Based on the data model proposed by Codd in 1970 The relational model proposes to organise the data using relations (basically tables): Each relation has a name Each relation is made up of named attributes (columns) of data Each relation contains tuples the tuples contain one value per attribute

12 Motivation for the relational model Application programs should not be affected by modifications to the internal data representation (changes to file organisation, access paths etc.) Deal with the redundancy problems and the consistency. For this the notion of normalised relations is crucial!

13 Terminology Relation: a table with columns and rows. Attribute: a named column of a relation. Degree of a relation: the number of attributes it contains Domain: the set of allowable values for one or more attributes. Very powerful feature!!! (Even if street names and telephones are Strings they are un-comparable. On the other hand it makes sense to multiply the number representing the monthly rent with the number representing the number of months a property has been leased). Tuple: a row of a relation. Cardinality of a relation: the number of tuples it contains

14 Terminology

15 Mathematical relations D1={2,4} D2={1,3,5} D1xD2 = {(2,1),(2,3),(2,5),(4,1),(4,3),(4,5)} Attention: D1xD2 is different from D2xD1. A subset of D1xD2 is a relation (for example: R={(2,1), (4,1)} ) (D for domain) R can also be defined using conditions: R={(x,y) such that x is in D1 and y is in D2 and y = 1} S={(x,y) such that x is in D1 and y is in D2 and y = 2x} S={(2,1)} We can extend the definition of relation to three sets: a subset of D1 x D2 x D3 Or to n sets: D1 x D2 x x Dn = {(x1, x2, xn) such that x1 is in D1, xn is in Dn.}

16 Database relations A relation schema: a names relation defined by a set of attribute and domain name pairs: Attributes A1, A2, An with domains D1, D2, Dn. A relation schema: {A1:D1, A2: D2, An:Dn} A relation defined by a relation schema is a set of n-uples: (A1:d1, A2:d2,. An:dn) such that d1 is in D1, d2 is in D2, etc. A database relation schema is a set of relation schemas, each with a distinct name.

17 Exercise Define a relation as the subset of 7-uples of numbers where the first is 2 and the rest are odd numbers smaller than 21. Write down examples of such relation. Provide the relation schemas for the table view of the database representing the rental agency. For example, how would you write the four-uples composing the Branch relation? Do this for all relations and all tuples.

Database Technologies. Madalina CROITORU IUT Montpellier

Database Technologies. Madalina CROITORU IUT Montpellier Database Technologies Madalina CROITORU croitoru@lirmm.fr IUT Montpellier Part 2 RELATIONAL ALGEBRA Background notions I A database relation is a set. Sets can be refined: One can select a subset of elements