Instructor: Pavlos Pavlikas1 How Data is Stored Chapter 8

Instructor: Pavlos Pavlikas2 Data and Information Surname Baker Class C11 When data are put into structure, these become information

Instructor: Pavlos Pavlikas3 Database Is a (large) collection of data items and links between them, structured in a way that allows it to be accessed by a number of different applications programs. Examples Telephone Index School’s Student Hospital’s Patients Books Information Catalogue GenBank

Instructor: Pavlos Pavlikas4 The parts of a database Record: Is the basic unit of data stored in a data file. It is the collection of items, which may be of different data types, all relating to the individual or object that the records describe (i.e. A Student) Field: Is a part of a record designed to hold a single data item of specified type (i.e. Student’s Name)

Instructor: Pavlos Pavlikas5 Key fields Is the field within a record used to identify the record. Most datafiles will have a primary key, which is unique and used to identify the record.

Instructor: Pavlos Pavlikas6 Fields Records Primary Key

Instructor: Pavlos Pavlikas7 Data type Variable Type: In high-level languages describes the kind of data held by a variable. Field Type: Describes the kind of data stored as a field within a datafile

Instructor: Pavlos Pavlikas8 Manual filing systems Problems: We cannot obtain information that is held on several files Because the data is not shared it is difficult to update the information An information can be accessed only by one person at a time. If a file is put back in the wrong place, finding it again will be very difficult

Instructor: Pavlos Pavlikas9 Computerised databases Advantages Access information from several files Easy to update Rapid access of information Validation checks may be made on the data on entry.

Instructor: Pavlos Pavlikas10 Computerised databases Disadvantages If the computer breaks down, you are not able to access the details Easy to copy files. Data must protected by passwords Training is needed to use the system

Instructor: Pavlos Pavlikas11 Database management system (DBMS) DBMS is a software that can find data in a database, add new data and change existing data. Examples Microsoft Access SQL Server Oracle Paradox Database

Instructor: Pavlos Pavlikas12 Relational database Is a complex database structure to hold a variety of different data. Where data items are related to each other, they are linked together by pointers stored in the database

Instructor: Pavlos Pavlikas13 Relational database Table: is the name for each group of similar data with rows for each member of the entity and columns for each attribute. Query: is a question asked of the data in the database. Report: is the presentation of the selected data. Reports are ready for printing.