How to organized data?
Organizing and accessing data are two of the driving forces behind data management. Organizing data involves arranging data in storage so that they maybe easily accessed, accessing data refers to retrieving data from storage. Data organization and access are important determinants of how easily managers and users can obtain the information they need to their jobs. Since some organization and access schemes provide faster or more flexible ways to locate individual records than others, it is important for managers to anticipate what data they and their subordinates will need when designing files and database.
Data accessing methods:
There are three different types of accessing data:
- Sequential data access
- Direct data access
- Indexed sequential data access
Sequential data access:
Sequential data access is a method whereby the records of file are accessed in sequential order. The records in a sequential file appear one after another in the order in which they were entered into the computer and subsequently stored on the medium. Access to any record requires access to all of the preceding records. Magnetic tape is a storage medium that is sequential in nature. To access a particular record on magnetic tape, you must read all of the preceding records first. You could use the sequential access method to record the individual student grades each week because you must access and update all of the records of the student anyway.
Direct data access:
Direct access also called random access is a method in which the records in a file are stored and accessed in a random order. A direct access file has key, called a key field or access key, that lets the computer locate, retrieve and update any record in the file without reading each preceding record. A key field is a field that uniquely identifies a record. Account numbers, employee identification number and social security numbers are examples of key fields.
Indexed sequential data access:
Third and final method of accessing data is Indexed sequential data access file processing allows both sequential and direct access of a record in a file. An Indexed sequential file can bed setup in many ways. Basically records are stored sequentially when the Indexed sequential file is created. However, where records are added to a file, they are stored out of sequence in an overflow area.
The computer keeps an index of the key fields from each record. It automatically sorts and updates the index to allow both sequential and direct access. Then it searches the index by key field to access a record. When it finds the key field, it can access the record directly using an address associated with the first key field in the sorted indexed order and follows the rest of the index in sequential order. The sorted index allows the computer to find records in sequence no matter where they are physically located on a disk. In practice, multiple indexes usually narrow the location of each record. This type of file access does not work with tape is a sequential access medium only.