Two hours UNIVERSITY OF MANCHESTER. January Answer any THREE questions. Answer each question in a separate book

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1 Two hours UNIVERSITY OF MANCHESTER Database Architecture Models and Design January 2004 Answer any THREE questions Answer each question in a separate book The use of electronic calculators is not peritted. [PTO]

2 2 1. a) Different ters ay be used for the sae concepts in SQL and relational algebra. What are the relational algebra ters corresponding to the following SQL ters: i) table description; i iv) table; row; colun. (8 arks) b) Answer the following questions on keys i) What is eant by a super key, a candidate key, a priary key, a foreign key and a coposite key; i iv) What is eant by referential integrity with respect to a foreign key; Describe three strategies for aintaining referential integrity when data is changed or deleted. colun. Assue that every student takes at least one odule. Write SQL to create a view called AvgMark that gives the ID of each student, and the average ark of that student across all of the odules that they take. (3 arks) Say why the AvgMark view is not updateable. (1 ark) c) Using the relations and the AvgMark view, write SQL queries answering each of the following: i) Return the ID and nae of all students whose average ark is higher than the average ark of the student whose ID is S1. (2 arks) Return the ID and nae of ebers of staff all of whose tutees (i.e., students who they tutor) have an average ark of less than 40. (4 arks)

3 3 2. Consider the following table for an exa adinistration syste: EXAM(studentId, studentnae, exaid, exadate, exatitle, exaroo, exainernae, exainerjobtitle, speciality, invigilatornae, invigilatorjobtitle) A student takes any exas. Each exa has an invigilator who is responsible for the exaination roo and an exainer who sets and arks it. The invigilator is responsible for the sae roo, and only that roo, throughout the exa period. The exainer has a particular acadeic speciality. Exainers and invigilators are ebers of staff and have a job title (teaching assistant, lecturer, professor etc.). As an alternative to the exaid, the exa title and date together identify a particular exa. a) Write down the functional dependencies which apply to the situation. For full arks the FDs you produce should for a inial set. (6 arks) b) Explain why the table is unnoralised, and why this is likely to cause serious probles when the database is updated. (4 arks) c) Convert the table into Boyce-Codd Noral For, justifying why the resulting tables are in BCNF, and have the lossless join property. Clearly identify the priary, candidate and foreign keys. (7 arks) d) Suggest how generalisation could be used to iprove the odel of the world which the noralised relations represent. (3 arks) [PTO]

4 4 3. The following is an EER odel for a Property Agent s Database. nae Person personid n offer price offers to buy propertyid nu of roos Property price lease duration o ortgage copany sells Tenant n Owner 1 1 owns rents a) Explain precisely how the Person, Tenant, and Owner entities are related. (2 arks) b) How could a siilar concept be expressed in Java? Why would it not be exactly the sae? (2 arks) c) Map the odel to a relational schea, showing the priary and foreign keys in each relation. Show two different ways of apping the owns and sells relationships. Considering that only the owner of a property can sell it, and that it ay not be for sale, which apping is better? (8 arks) d) Use the exaple to illustrate soe of the techniques used to tune the perforance of a relational database. In particular, suggest two different ways to speed up the join between Property and Tenant, assuing that a property usually has only one tenant if any. Give the relative erits and drawbacks of your proposed solutions. (8 arks)

5 5 4. a) What is the eaning of ACID properties of transactions? (2 arks) Describe how transactions are used for following. Illustrate with exaples of transactions for booking a holiday based on the Sweeney Tours laboratory exercise. i) concurrency control (5 arks) recovery anageent (5 arks) i integrity constraint anageent (2 arks) b) Stockport Vegetable Market has a collection of nubered stalls. Each stall has a nae (unique) and sells a range of vegetables (each of which have a nae). Each stall sells each vegetable at their own particular price. Each of the any fars grow soe (but not all) the vegetables, but a vegetable ust be grown by at least one far. Many fars supply vegetables to any stalls. Each far has a nae (unique) and address. Each stall buys each vegetable fro only one far at a particular price that they negotiate. A far supplies a nuber of vegetables to each stall. Draw the EER diagra that odels this scenario. (6 arks)