IGCSE Information Communication Technology (ICT) Syllabus code Section 5: Data types

Transcription

1 IGCSE Information Communication Technology (ICT) Syllabus code 0417 Section 5: Data types

2 At the end of this Unit students will be able to: (a) identify different data types: logical/boolean, alphanumeric/text, numeric (real and integer) and date (b) select appropriate data types for a given set of data: logical/boolean, alphanumeric/text, numeric and date (c) describe what is meant by the terms file, record, field and key field (d) describe different database structures such as flat files and relational tables including the use of relationships, primary keys and foreign keys (e) state the difference between analogue data and digital data (f) explain the need for conversion between analogue and digital data What is a database? Databases are designed to offer an organized mechanism for storing, managing and retrieving information. They do so through the use of tables. In order for a database to be truly functional, it must not only store large amounts of records well, but be accessed easily. In addition, new information and changes should also be fairly easy to input. Lets take the example of a phone book. The phone book contains several items of information name, address and phone number about each phone subscriber in a particular area. Each subscriber's information takes the same form. In database parlance, the phone book is a table which contains a record for each subscriber. Each subscriber record contains three fields: name, address, and phone number. The records are sorted alphabetically by the name field, which is called the key field. Database Terminology What is a table? A single store of related information. A table consists of records, and each record is made up of a number of fields What Is a record?

3 A table consists of records, and each record is made up of a number of fields. A record contains all the information about a single 'member' of a table. In a student s table, each student's details (name, date of birth, contact details, and so on) will be contained in its own record. What is a field? Fields describe a single aspect of each member of a table. A student record, for instance, might contains a last name field, a first name field, a date of birth field and so on. What is a Key Field? Keys are crucial to a table structure for many reasons, some of which are identified below: They ensure that each record in a table is precisely identified. They help establish and enforce various types of integrity. They serve to establish table relationships. Primary key will uniquely identify each record. It may or may not provide information about the record it identifies. It must not be Null-able, that is if it exists in a record it cannot have the value Null. It must be unique. It cannot be changed. Let s take the example of Student s database in a School Type When a database is designed, all the fields are set to accept a particular data type. This helps check for the wrong type of data being entered and makes sure the data is stored as efficiently as possible. It also means it will be sorted correctly.

4 Alphanumeric/text fields A field of this data type will accept text, numbers and symbols Example include: Surname: Smith Forename: Paul Car Registration Number: B1234XY Numeric fields A field of this data type is used to store numbers. Number fields are used to store numbers because the data will be sorted correctly (i.e. the numerical data 2,3,20,30 would be sorted as 2,20,3,30 if it was stored in a text field) There are two types of numeric field you need to know about: Real - used for decimal numbers such as 3.4, and 6.0 etc. Real numbers can be formatted as currency (i.e. 5.67) or to a fixed number of decimal places (i.e. entering into a real number field formatted to two decimal places would mean it appeared as 3.14) Integer - used for whole numbers. Logical/Boolean fields A field of this data type will only let you enter a 'Yes' or a 'No', Male or Female, On/Off. Date/Time A field of this type stores days, months and years and Time. Example include 15 August 2001, :15 PM 22:15

5 Databases There are several common types of databases; each type of database has its own data model (how the data is structured). They include; Flat Model, Hierarchical Model, Relational Model and Network Model. The Flat Model Database In a flat model database, there is a two dimensional (flat structure) array of data. For instance, there is one column of information and within this column it is assumed that each data item will be related to the other. For instance, a flat model database includes only zip codes. Within the database, there will only be one column and each new row within that one column will be a new zip code. A flat file is a static document, spreadsheet, or textual record that typically contains data that is not structurally related. Flat files are called so because there is little that can be accomplished with the information contained in them other than reading, storing, and sending. Flat files are typically basic data sets that are used for configuration data storage for applications and programs. The average computer user will not typically see them much. There are basic address book-like examples of a flat file that can be used, but modern users typically desire a more robust and sophisticated method of calling up their information than to rely on the

6 limited capability of a flat file structure. Flat files are commonly used by and found in database management systems, typically belonging in and organized into flat file databases. A flat file database is really nothing more than an organization criterion assigned to a sample set of flat files. The Hierarchical Model Database The hierarchical model database resembles a tree like structure, such as how Microsoft Windows organizes folders and files. In a hierarchical model database, each upward link is nested in order to keep data organized in a particular order on a same level list. For instance, a hierarchal database of sales, may list each days sales as a separate file. Within this nested file are all of the sales (same types of data) for the day. The Relational Model The relational model is the most popular type of database and an extremely powerful tool, not only to store information, but to access it as well. Relational databases are organized as tables. A table can have many records and each record can have many fields. Tables are sometimes called a relation. For instance, a company can have a database called customer orders, within this database will be several different tables or relations all relating to customer orders. Tables can include customer information (name, address, contact, info, customer number, etc) and other tables (relations) such as orders that the customer previously bought (this can include item number, item description, payment amount, payment method, etc). It should be noted that every record (group of fields) in a relational database has its own primary key. A primary key is a unique field that makes it easy to identify a record. Relational databases help maintain data integrity and reduce data redundancy.

7 Data integrity refers to data that is accurate or correct or complete or as up-to-date as possible. Data redundancy is a data organization issue that allows the unnecessary duplication of data within a database. Difference between analogue data and digital data Analogue data is represented in a continuous form, as contrasted with digital data having discrete values. Data that is recorded in a form that is similar to its original structure. Contrast with digital data, Analogue signals use continuously variable electric currents and voltages to reproduce data being transmitted. Need for conversion between analogue and digital data Since data is sent using variable currents in an analogue system, it is very difficult to remove noise and wave distortions during the transmission. For this reason, analogue signals cannot perform high-quality data transmission. On the other hand, digital signals use binary data strings (0 and 1) to reproduce data being transmitted. Noise and distortions have little effect, making high-quality data transmission possible.