Now, please open your book to page 60, and let’s talk about chapter 9:

How Data is Stored.

1. In this chapter, it talked about DATABASE, what is a database?

2. What are the parts of database?

3. Record design. (Key fields)

4. Manual filing systems.

5. Computerized Databases. (Advantages and disadvantages.)

6. File organization. (Serial, sequential and random files.)

7.Methods of accessing files. (Serial, sequential and direct accesses.)

8. Types of files. (Master, transaction and backup or security files.)

9. The grandfather-father-son principle.

10. Fixed and variable length fields.

11.Common file processes. (File updating, insertions, deletions and amendments.)

12….Lucky last! File manipulation. (Sorting, merging, file interrogation and data analysis)

This chapter is a long chapter, but don’t worry, we will get it through. There are few key points to look at before we start to get on with this chapter.

Chapter 9: How Date is Stored

1. What is a DATABASE?

A database is an organized collection of information or data.

Putting information into a computer database give you far more flexibility in organizing, displaying and printing that information.

2. The parts of database.

Files: A computer’s equivalent of the complete box is a file. The computer’s file is usually stored on a disk, which may be optical or magnetic.

Records: These are the details and information, the computer database will display one record on the screen at a time.

Fields: These are the headings or categories. Each “item” of information on the computer record is known as a field, and it consists of two parts: the field name and the field data. The field names are the words “Title”.

Figure 9.1 shows the relationship between files, records and fields.

3. Record design. (Key fields.)

Modern databases give you freedom to design your own records. They give you an empty screen on

which you can add the field names, fields and other background text such as the title.

Key fields is a field that may be used to search a file, they are unique.

4. Manual filing systems.Please take a look figure 9.3 at the left-hand corner of page 62.

As you can see, some of the data is the same on each file.

This is called data duplication and is one of the main problem with manual filing systems.

Data duplication means that more space is taken up by the files and more work is needed to retrieve the information.

5. Computerized databases.

There are 5 main advantages and 3 main disadvantages that they mentioned in the

text book on the top of page 63.

Let’s take a closer look at them.

6. File organization.

There are several methods you can use to organize files.

Serial files: With serial file, the records do not follow each other in any particular order, so if another record needs to be added it can just be added onto the end of the file.

Sequential files: These files are like serial files except that the records are held in a certain sequence. The user can decide what kind of order the file is going to be in. e.g.: number sequence.

Random files: They are not stored in any order on the disk surface, and they have to be stored on disk.

7. Methods of accessing files.

Serial access: To read a serial file, a computer has to read each record until it reaches the one required.

Sequential access: With sequential access the records are in order, so if just one record is required then the method is slow but if all the records are required then it is very fast.

Direct access: With direct access files, it is possible to go directly to a record without having to look at any other records first. You can access both sequential and random access files directly.

8. Types of file.There are various types of file.

Master files: A master file is the most important file since it is the most complete and up-to-date version of a file. If a master file is lost or damaged and it is the only copy, the whole system will break down.

Transaction files: Are used to hold temporary data which is used to update the master file.Transactions can occur in any order, so it is necessary to sort a transaction file into the same order as the master file before it is used to update the master file.

Backup or security files: Backup copies of files are kept in case the original is damaged or lost and cannot be used. This is a very important point with master files as it is controlling the whole system.

9. The grandfather-father-son principle.Basically, three generations of file are kept. The oldest master file is called the grandfather file and it is kept with its transaction file. These two files are used to produce a new master file called the father file which, with its transaction file, is used to create the most up-to-date file, called the son file.

This is used to stop the master file from being destroyed by an inexperienced user, a power failure or a fire.

The transaction

file

TheOldest

File(Grandfather)

Merge

Anothertransaction

file

AnotherMaster

file(Father)

Merge TheNewest

file(Son)

10. Fixed and variable length fields.

Fixed length field: Is one where the length of the field has been decided in advanced.

Variable length field: Where take up only as much space as the data requires.

We are almost there! Let’s go!

11. Common file processes.File updating: This involves bringing a file up-to-date with any changes that have occurred since it was last updated.

Insertions: The key-in of the new information. Be careful with the differences between updating and insertions.

Deletions: The remove (delete) of the information. It is like to “take-off” or to erase a information.

Amendments: “To amend” means to change, so this is to make some changes with the information. I find this one confusing..do you? I think it’s almost the same as updating!

Mr. Millard, would you explain to us?

And…the last one!!!

12. File manipulation.Sorting: Often a field needs to be sorted into a particular order, it is possible to sort according to several fields, but the commonest one is sorted the field in alphabetical order.

Merging: To combine the contents of two files to form a single file.

File interrogation: This involves getting information from a file. Fields are selected and the computer then searches through the records, finding all the records with matches on the field/s being used for the search.

Data analysis: Some databases allow the the data to be analyzed in some way once it has been entered. E.g. Bar charts, pie charts and line graphs.

Thank you all for watching, reading and listening!

Presented by Connie and Ting-Ting