Summary Points
- Batch file access methods require transactions to be gathered for
processing at one time.
- Online file access methods provide the ability to retrieve data and
update it at any time.
- In sequential file design, all data is stored in sequential order on a
master file; it must be ordered by some key field. Transactions to be processed against
the master file are stored in a transaction file. Transactions are usually collected and
processed against the master in one batch. During processing, transactions are matched
against the master file, and updates to the master file are made by writing a new master
during processing. The entire master file must be read when sequential processing is used.
- Batch access methods are generally used with sequential file design.
- In direct-access processing, records are accessed according to their
key. The computer determines the location of the record on the disk by a transformation
process on the key or by using a directory. Once the physical address is known, the record
can be retrieved.
- Direct-access file designs are accessed using online methods.
- Indexed-sequential processing is used when the same file may be required
for sequential processing and for single-record updates. A primary key is used to identify
each unique record, and records are stored in sequence according to the primary key.
Secondary keys are set up for those fields used to gain access to the file. The computer
uses the key value to determine the approximate physical location of the record (or
records), and then reads the records sequentially until the desired one is found.
- A data base is a grouping of data elements structured to fit the
information needs of all departments of an organization. The data base reduces data
duplication and increases efficiency and flexibility.
- Data within a data base can be structured in many ways. Four ways are
the simple structure, the hierarchical structure, the network structure, and the
relational structure.
- In a simple structure, records are arranged sequentially. Inverted
structures are used to index files with simple structures according to attributes which
are characteristic fields.
- In a hierarchical structure, a given parent element may have many
children, but a given child can have only one parent. In network structures, on the other
hand, a parent can have many children, and each child can also have more than one parent.
- The newest type of data-base structure, the relational structure, has
data elements placed in tables called relations. The rows represent records and the
columns contain fields.
- A data-base management system is a set of programs that provides a
method of arranging data to limit the duplication of data.
For the Unit Examination you should be able to:
- Describe the difference between Batch and Online processing.
- Explain briefly each of the following file designs and under what
circumstances they are used:
- Explain the benefits of using a Database.
- List 4 different ways a database can be structured.
- Describe what a primary key is and why they are used.
Last Updated Jan.6/99