Data has to be put into a database, found again, looked after and often passed on to other systems. The specification calls these capturing, selecting, managing and exchanging data.
Capturing Data
Definition
Data capture is the collection of data and its entry into a computer system, either typed in by a person or read automatically by a device.
Key Point
| Method | How it works | Typical use |
|---|---|---|
| Forms, on paper or online | A person types the data in. An online form can validate each field as it is entered | Registering a customer, placing an order |
| Optical Mark Recognition (OMR) | Detects the position of marks made on a pre-printed form | Multiple-choice answer sheets, lottery tickets |
| Optical Character Recognition (OCR) | Converts an image of printed or handwritten text into characters | Postcodes on letters, vehicle number plates |
| Magnetic Ink Character Recognition (MICR) | Reads characters printed in magnetic ink | Account details on cheques |
| Barcodes and QR codes | A scanner reads a printed pattern that stands for a code | Shop tills, tickets, parcel tracking |
| Magnetic stripe, chip and contactless cards | A reader takes the data stored on the card | Bank cards, door entry, travel cards |
| Sensors | Measure a physical value automatically at set intervals | Temperature logging, counting vehicles |
Key Point
Choosing a capture method:
• Automatic methods are faster than typing and make fewer errors, because nobody has to copy the data
• They need special equipment, and the data has to be prepared in a fixed format
• Typed data should be validated, for example with range, length, format and presence checks, so that values which are not sensible are rejected
• Automatic methods are faster than typing and make fewer errors, because nobody has to copy the data
• They need special equipment, and the data has to be prepared in a fixed format
• Typed data should be validated, for example with range, length, format and presence checks, so that values which are not sensible are rejected
Selecting Data
Selecting data means retrieving only the records and fields that are wanted. In a relational database this is done with a query, either written in SQL (section d) or built visually with Query by Example (section f). A query states the fields to show, the table or tables to use, the criteria that records must meet and the order of the results.
Managing Data
Definition
A Database Management System (DBMS) is the software that creates and manages a database. It sits between the stored data and the users and applications, so they never work with the underlying files directly.
Key Point
What a DBMS does:
• Hides the physical structure of the data, so programs do not depend on how it is stored
• Runs queries and updates on behalf of users and applications
• Controls access: each user can be given rights to view or change only certain data
• Enforces integrity rules such as validation, primary keys and referential integrity
• Manages many users at once, using record locking so that their updates do not clash
• Provides backup and recovery, so data can be restored after a failure
• Hides the physical structure of the data, so programs do not depend on how it is stored
• Runs queries and updates on behalf of users and applications
• Controls access: each user can be given rights to view or change only certain data
• Enforces integrity rules such as validation, primary keys and referential integrity
• Manages many users at once, using record locking so that their updates do not clash
• Provides backup and recovery, so data can be restored after a failure
Exchanging Data
Data often has to be passed from one system to another, for example from an online shop to the courier that delivers its parcels. The two systems are unlikely to store data in the same way, so it is exchanged in a standard format that both understand.
Definition
Data exchange is the transfer of data between different systems in a format that both have agreed on.
Key Point
| Format or method | Description |
|---|---|
| CSV (comma-separated values) | A plain text file with one record per line and a comma between fields. Simple and widely supported, but it holds no information about data types or structure |
| XML (eXtensible Markup Language) | Text in which each item of data is enclosed in named tags, so the file describes its own structure |
| JSON (JavaScript Object Notation) | Text that holds data as pairs of names and values. More compact than XML and widely used by web applications |
| EDI (Electronic Data Interchange) | The computer systems of different organisations exchange documents such as orders and invoices automatically, in an agreed format, with nobody re-typing them |
Worked Example
Worked Example: One Record in Three Formats
CSV:
XML:
JSON:
The CSV line only makes sense if the receiving system already knows the order of the fields. XML and JSON name every field, so they are easier for another system to interpret.
CSV:
text
S001,Alice,12
xml
<student>
<id>S001</id>
<name>Alice</name>
<year>12</year>
</student>
json
{ "id": "S001", "name": "Alice", "year": 12 }