[1] File organisation and access

Benefits of a serial file organization

- cheap - fast

What are the drawbacks of a sequential access?

- difficult to update/delete individual files - long access time, as read and write operations happen sequentially

Drawbacks of a serial file organization

- file requires a preset format for the input of data - slow access rate

Which files use direct access

- sequential files with index files - random access files

Which files use sequential access?

- serial files - sequential files

What are the benefits of a sequential access?

- simple organisation - easy to modify

How does the program add a new record to a file using direct access?

- the key field is hashed to produce the home location - if the home location is free, the record is inserted - if the home location is not free, the overflow method is used to find a free location to store the record - if the file has no free location, the record cannot be stored

When is a sequential access used?

- when every file needs to be processed - there is a high hit rate

When is a direct access used?

- when only an individual file needs to be accessed - there is a low hit rate

What is a record?

A collection of fields containing data values

What is file access

A method by which a record/field is read from/written to

What is a field?

A single piece of data

Drawbacks of a sequential file organisation

Adding/deleting/editing requires making a new file

What are the drawbacks of direct access?

Easily damaged

What are the benefits of direct access?

Easy to update/delete individual records

Benefits of a random file organisation

Faster access speed

Drawbacks of a random file organisation

Less efficient in the use of storage space

Describe a direct access

Records are accessed directly without accessing other records (e.g. CD)

Describe a sequential file organisation

Records of data are organised in a given order by means of a key field (e.g. vinyl albums)

Describe a random file organisation

Records of data are organised using a record key and can be accessed randomly (e.g. employee database)

Describe a serial file organization

Records of data are organized in the order they were added to the file (eg applications error-log file)

Benefits of a sequential file organisation

Suitable for long-term use

What is file organisation?

The way in which fields are organized/structured in a file

Describe a sequential access

records are accessed one after another (e.g. magnetic tape)