Data hierarchy refers to the systematic organization of data, often in a hierarchical form. Data organization involves fields, records, files and so on.
A data field holds a single fact or attribute of an entity. Consider a date field, e.g. "September 19, 2004". This can be treated as a single date field (e.g. birthdate), or 3 fields, namely, month, day of month and year.
A record is a collection of related fields. An Employee record may contain a name field(s), address fields, birthdate field and so on.
A file is a collection of related records. If there are 100 employees, then each employee would have a record (e.g. called Employee Personal Details record) and the collection of 100 such records would constitute a file (in this case, called Employee Personal Details file).
Files are integrated into a database. This is done using a Database Management System. If there are other facets of employee data that we wish to capture, then other files such as Employee Training History file and Employee Work History file could be created as well.
An illustration of the above description is shown in this diagram below.
The following terms are for better clarity.
With reference to the example in the above diagram.
Data field label = Employee Name or EMP_NAME
Data field value = Jeffrey Tan
The above description is a view of data as understood by a user e.g. a person working in Human Resource Department.
The above structure can be seen in the hierarchical model, which is one way to organize data in a database.
In terms of data storage, data fields are made of bytes and these in turn are made up of bits.