Management Information Systems Charles Parker 2nd Edition Chapter 7: Data Management Prepared By: Hamad Raza (Lecturer GCUF)

Data Access & Organization Methods Organizing & accessing data are two of the driving forces behind data management. Organizing data involves arranging data in storage so that they may be 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 do their jobs. As some organization & 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 databases.

Data Access & Organization Methods There are different types of Data Access & Organization methods: Serial: The simplest organization scheme is serial. With serial organization, records are arranged one after another, in no particular order. Serial organization is commonly found with transaction data, where records are created in a file in the order in which transactions take place. For Example: File consisting of daily purchase & payment transaction data. It may often used to update records in a master account file at night.

Data Access & Organization Methods Serial:

Data Access & Organization Methods Sequential: Sequential 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. The field on which records are sequentially organized is often called primary key. For Example: 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.

Data Access & Organization Methods Indexed: Records in an indexed file may be physically stored sequentially, serially, or even randomly. A second file known as an index – makes it possible to access individual records directly, no matter how the records are physically stored. To directly access individual records, users consult an index to select the records of interest.

Data Access & Organization Methods Indexed-Sequential: Indexed sequential organization is a file organization scheme that allows both sequential & direct access to data. Thus file organized in this manner must be on a direct access storage device (DASD) such as disk. With indexed-sequential organization, records are usually physically arranged on a storage medium by their primary key, just as they are with sequential organization. The difference is however, that an index also exists for the file, it can be used to look up & directly access individual records.

Data Access & Organization Methods Direct Access: Direct access is also called random access is a method in which the records in a file are stored and accessed in random order. A direct access file has a 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 each record. Account numbers, employee identification number and social security numbers are examples of key fields.