1. Desirable features in an information system Integrity Referential integrity Data independence Controlled redundancy Security Privacy

2. File systems Sequential or serial Indexed sequential Relative

3. Database definition a computerised record-keeping system used by a range of users who have different requirements –minimal enquiries –in-depth updating –restructuring A well-implemented database will have data integrity, data independence, controlled redundancy, security and privacy, for all users.

4. Uses of a Database Generally used for on-line transaction processing (OLTP) Data Warehouses are a hybrid of databases which are used for On-line analytical processing (OLAP)

5. Structure of a database External Schema Conceptual Schema Internal Schema Physical Schema

6. External level Level visible to user Multiple views of the system –e.g. View an order - see limited product and customer information Only the database Administrator may access the whole database at this level

7. EXTERNAL SCHEMA Each external view is defined by means of an external schema Provides definitions of each external view. Written in a Data Definition Language individual to the user accessed through a 3GL, a query language or a special purpose forms or menu-based language

8. Conceptual level CONCEPTUAL - represents the entire information content of the database Consists of multiple types of conceptual record. This level preserves the data independence of the database. CONCEPTUAL SCHEMA - defines each of the various types of conceptual record, in a conceptual Data Definition Language.

9. Internal level INTERNAL - a low-level representation of the entire database; it consists of multiple occurrences of multiple types of internal record. It is the stored record, inasmuch as it contains all but the device-specific information on the storage of the database. PHYSICAL - the physical device and block addresses for each of the records.

10. Mappings Each level maps onto adjoining levels conceptual / internal mapping specifies how conceptual records and fields are represented at the internal level Changes can be made in the internal level without affecting the conceptual level external / conceptual mapping defines the correspondence between an external view and the conceptual view

11. DBMS - Database Management System software handling access to the database allows both the database administrator and all users the access to the database to which they are entitled

12. How requests are processed User issues request (e.g. through SQL) DBMS intercepts and analyses request DBMS inspects user's external schema, external to conceptual mapping, conceptual schema, conceptual to internal mapping and the storage structure definition. DBMS executes operations on stored database.

13. DATABASE ADMINISTRATOR (DBA) Decide on the storage structure and access strategy Liaise with the users Define security and integrity checks Define a backup and recovery strategy Monitor and respond to performance

14. Utilities used by the DBA Load routines Dump/Restore routines Reorganisation routines Statistics routines Analysis routines Data dictionary (containing METADATA, which gives data descriptions and mappings)

15. Relational database Data is independent from programs and from other data Data is represented in TABLES rather than files. (one entity corresponds to 1 table) Column headings are described as DOMAINS. (i.e. attributes) Items of information as TUPLES or ROWS rather than records (i.e. occurrences of the entity)

16. Definitions A RELATION is a collection of semantically related information, usually containing a unique key. A RELATION = a Table FOREIGN key - a key to a different relation that is used as non-key data in this relation. (i.e. the enforcing field in the relationship) SIMPLE key - uses one item from the row COMPOUND key - uses more than one item / attribute Unnormalized data - contains headings, footings, differing number of occurrences for different fields.

17. Properties of a relation Third Normal form (TNF) test. –All row entries are non-divisible (atomic) - i.e. no such thing as arrays –All entries in a particular column are drawn from the same set (i.e. no such thing as redefines)

18. Normalisation of data Collect all documents to be entered/produced Represent documents in unnormalized form Choose and identify key items, giving unnormalized data + keys Separate out repeating groups -> 1st Normal Form (1NF) Separate out part key dependencies -> 2nd Normal Form (2NF) Separate out inter-data and inter-key dependencies -> 3rd Normal Form (TNF) Apply TNF tests Optimise by combining relations with identical keys Apply TNF tests again

19. Relational database This is a database that is perceived by its users as a collection of tables. Each table can define an ENTITY Entities can be related through RELATIONSHIPS Relationships are implemented by use of foreign keys in tables Each column has a unique name within the table All rows are distinct (no two are the same) Row or column order is not significant Every relation must have a key

20. Operations in SQL Tables are created by the CREATE TABLE statement: CREATE TABLE DRIVERS (DRIVER_NUMBER SMALLINT NOT 0, DRIVER_NAME CHAR(20), HOME_DEPOT CHAR(6), VEHICLE_TYPE etc... Tables can be changed: ALTER TABLE DRIVERS ADD OTHER_ALLOWANCES CHAR(6); and deleted: DROP TABLE DRIVERS;

21. Operations in SQL Tables can be joined together on fields which have the same attributes: SELECT DRIVER.*, VEHICLE.* FROM DRIVER, VEHICLE WHERE DRIVER.VEHICLE_TYPE = VEHICLE.VEHICLE_TYPE;

22. Implementation of desirable features Integrity –A field’s validation can be declared when the field is declared. If this validation is used, then the integrity of the field remains intact. –Entity integrity - No attribute participating in the primary key of a base relation is allowed to accept null values. –Domain constraints - what are the possible valid values that can be used?

23. Referential integrity –Through the propagation and use of foreign keys, no detail can be created where a master is needed, nor can a master be deleted without consent to the deletion of the details

24. Implementation of desirable features Data independence –The implementation of relational databases causes the external and conceptual schema to be data independent. The internal schema and the physical level are data dependent. Controlled redundancy –The relational model reduces redundancy at the conceptual level

25. SECURITY Legal, social and ethical considerations (e.g. Data protection act) Physical controls - locking of computer rooms Company policy Operational - e.g. password access rulings Hardware controls - e.g. privileged operating mode Limits on fields that users can see

26. Security and SQL SQL allows views to be created that only allow the view users access to a range or selection of values for particular fields; e.g. CREATE VIEW CORK_DRIVERS AS SELECT DRIVER_NUMBER, DRIVER_NAME, YEARS_SERVICE FROM DRIVERS WHERE HOME_DEPOT = "CORK"; This is a value-dependent constraint.

27. Security and Privacy in SQL Different users can be granted different access rights : GRANT SELECT, UPDATE (CREDIT_LIMIT, AMOUNT_OWING) ON TABLE CUSTOMER TO GRP_ACCNTS; GRANT SELECT ON VIEW CUSTOMER_TOTAL TO DEPOT_CONTROLLERS; The access types that can be granted are SELECT, UPDATE, DELETE and INSERT. Access rights can also be REVOKEd.

28. Security and SQL Field-dependent constraints can be imposed by omitting the field from the view. Views can also be presented so that they give totals only - not individual items: CREATE VIEW CUSTOMER_TOTAL AS SELECT CREDIT_LIMIT, AMOUNT_OWING FROM CUSTOMERS GROUP BY CREDIT_LIMIT

29. JOURNALLING An audit trail can be set up to follow operations on the database. This involves journalling of each, or a specific type of operation on the database or some part of it. The audit trail should specify the operation, the terminal from which it was invoked, the user, the date-time, the database, table, record and field affected, the old and new value of the field. The advantages of this are that it gives the auditors a way of tracing any discrepancies. However, it slows down the operation of the system considerably.

30. BACKUP SECURITY As well as the fact that the database administrator will ensure that the full database is backed up in a logical way, most databases have the COMMIT/ROLLBACK facility: Whenever a program updates the database, the update remains tentative only, until a COMMIT causes it to become permanent, or a ROLLBACK cancels it. ROLLBACK is only issued if an exception occurs

31. Internal level (relational) Internal schema (some Data Definition Language). Stored_DriverLength 41. Driver_numberBYTE(6), Offset 0, INDEX. Driver_NameByte(20), Offset 6. Driver_Home_depotByte(1), Offset 26. Driver_vehicle_typeByte(2), Offset 28. (**) Driver_empl_dateByte(8), Offset 30. Driver_TFAByte(2), Offset 38. Driver_Tax_TableByte (1), Offset 40.

32. Conceptual schema (some Data Definition Language) Driver. Driver_numberCharacter (6). Driver_NameCharacter (20). Driver_Home_depotNumeric (1). Driver_vehicle_typeCharacter (2). Driver_employment_dateDate Driver_TFANumeric 7 digits 2 decimal Driver_Tax_TableCharacter 1.

33. Subschema or External schema (COBOL) 01Driver-pay-table. 02 Driver_nopic x(6). 02 Driver_namepic x(20). 02 Driver_Vehicle_typepic xx. 02 Driver_TFApic 9(5)v99. 02 Driver_Tax_Tablepic A. 02 Driver_Employ_datepic 99/99/9999.

34. External schema 01Driver_location_table. 02 Driver_nopic x(6). 02 Driver_namepic x(20). 02 Driver_Vehicle_typepic xx. 02Driver_Home_depotpic 9.

35. Data Warehouse Definition - a collection of current and historical operational data stored for use in executive support systems (a.k.a. executive information systems EIS) and decision support systems DSS. Purposes –Growing demand that executives and management have rapid, easy access to operational data for planning and decision making –Diversity of format and location of historical data

36. Storage of non-standard data types Pictures, Video clips, Sound clips Can be done on a relational database. These data types are seen conceptually as just another data type. Only data is held on them - i.e. a video clip can be held on a relational database, but separate functionality must be provided to play it - this also applies to sound and still pictures. Oracle and Informix call these databases “universal” databases. IBM call them “extenders” to DB2.

37. Distributed databases Databases can now be distributed over different computers and operating systems by the use of middleware –Open DataBase Connectivity (ODBC) In order for database requests to be passed from one computer to the other, special software is supplied that will translate the client computer’s request into a format understood by the target server computer. The reply is then converted back. This layer of software is called middleware.

38. ODBC This middleware provides only database connectivity - there is a generally accepted ODBC (open database connectivity) standard. This increases scalability. ODBC connects to relational database management systems, but not to flat files, thereby excluding a lot of legacy systems. All the major RDBMS vendors are offering software to link their databases to the Web. Primary examples are Oracle’s Network Computing Architecture and Informix’s Universal Web Architecture