Relational databases: organisation Logical schema: – Entities – a specific category of data about which a database needs to store data e.g. Definitions table is an entity, Topic Area is an entity – Attributes – a property of an entity e.g. Terms is an attribute of the Definitions table – Relationships – the way in which entities in the database are related to each other Tables are the implementation of entities and consist of attributes and records.
Views of the database Different views have different purposes: – Tables (entities) – hold data in rows and columns Rows are called TUPLES Columns are attributes – Forms – set up for data entry – Queries – allow for questions to be asked of the database – Reports – allow for summaries and records to be extracted from the database in various ways for various purposes
Data entry screens A data entry screen is one that has been designed for a specific application. It is usually a form. It may include such items on the screen as: – Drop down/List boxes – for example, containing Country – Option buttons – for example, choosing Male or Female – Dynamic update of boxes based on previous selections – for example, when you select a customer, it only displays orders that only that customer has placed – Buttons on the screen specific to the application – Specific searches as required by the application
Reports and queries Every system is designed from the point of view of information requirements – what information does the user want to get from the system? There are two aspects of a database that produce information – Queries and Reports. – Queries – questions you can ask of the database. These need to be tailored to the specific requirements of the user. – Reports – displaying information in a presentable and understandable format – possibly with a view to printing. Each must be designed in conjunction with the user and the end requirements.
Queries Query by example These allow criteria to be typed and a filter to be applied to exclude unwanted data. Query storage Queries can be static or dynamic. Static queries are stored with the database and do not change. They are used frequently. Dynamic queries are those that have their criteria changed frequently. Usually they are adapted from a general query. Complex queries These are queries with more than one parameter (criteria). Use of: – AND, OR, NOT – For example: Name is SMITH and lives in ASHFORD
Queries: SQL Queries can be used to retrieve information from a database through the use of a structured query language (SQL). SQL commands include: – SELECT (field or fields) – FROM (table/s) – WHERE (operators – relational and logical) – ORDER BY (sort)
Data modelling: databases Schematic diagrams (ERD) – map entity types, the relationships between them and the characteristics of the relationships between entity types Normalisation – reduces data redundancy by ensuring that each table can be edited and manipulated separately – INF and DKNF
Modelling: data dictionaries A data dictionary contains descriptions of, and other information about, the structure of the data held in a database (metadata) It contains information about the tables: – Minimum is: fieldname, data type, size, description. May also include keys, indexes, joins, referential integrity etc. It contains information about the database itself: – Permissions and users The data dictionary should be stored as a table in the database. (It is usually hidden from view!)
DBMS A database management system (DBMS) is a piece of software that is used for the creation, control, access and management of a database. The DBMS acts as an interface between the database (raw data) and the application programs that use the database. Microsoft Access, Dbase and File Maker Pro are examples of database management systems available for microcomputers. The major function of the DBMS is to handle access to the database, that is, storage and retrieval of data. The DBMS is a shell – data is added to the database when the shell has been set up. Mac To end show: On a, press ESC. On a PC, close this window.