A collection of records pertaining to one of the main subjects of an information system, such as customers, employees, products and vendors. Master files contain descriptive data, such as name and address, as well as summary information, such as amount due and year-to-date sales. Contrast with transaction file.

Following are the kinds of fields that make up a typical master record in a business information system. There can be many more fields depending on the organization. The "key" fields below are the ones that are generally indexed for matching against the transaction records as well as fast retrieval for queries. The account number is usually the primary key, but name may also be primary. There can be secondary indexes; for example, in an inverted file structure, almost all the fields could be indexed. See transaction file for examples of typical transaction records.

       EMPLOYEE MASTER RECORD
  key  Employee account number
  key  Name (last)
       Name (first)
       Address, city, state, zip
       Hire date
       Birth date
       Title
       Job class
       Pay rate
       Year-to-date gross pay

       CUSTOMER MASTER RECORD
  key  Customer account number
  key  Name
       Bill-to address, city, state, zip
       Ship-to address, city, state, zip
       Credit limit
       Date of first order
       Sales-to-date
       Balance due

       VENDOR MASTER RECORD
  key  Vendor account number
  key  Name
       Address, city, state, zip
       Terms
       Quality rating
       Shipping method

       PRODUCT MASTER RECORD
  key  Product number
  key  Name
       Description
       Quantity on hand
       Location
       Primary vendor
       Secondary vendor