Record Management Services (RMS)

RMS is the acronym of Record Management Services in OpenVMS. RMS is the data management subsystem of the operating system. RMS gives the facility of efficient and flexible storage, retrieval, and modification of data on disks, etc. RMS may be implemented through the File Definition Language (FDL) interface.

What is a File?

A computer file is an organized collection of data stored on a mass storage volume and process by a CPU. Data files are organized to accommodate the processing of data within the file by an application program. The basic unit of electronic data processing is the record. A record is a collection of related data that the application program processes as a functional entity. Records are made up of fields, which are sets of contiguous bytes. A byte is a group of binary digits (bits) that are used to represent a single character.

 

The records in a file must be formatted uniformly, i.e. they must have some defined arrangement of the record fields including the field length, field location, and the field data type. In order to process the record files one must have an arrangement of the record fields handy. The file organization is the manner in which data is recorded within a file. The file organization, together with the applicable storage medium, determines what techniques should be used to access data. RMS supports two methods of record access: sequential access and direct access. Direct access includes relative access (using the relative position of a record) and indexed access (using an indexing key within the record). Below is the table to look at the methods in which the records can be accessed:
 

Access Method	Description
Sequential Access	Records are stored or retrieved one after another starting at a particular point in the file and continuing in order through the file.
Relative Record Number Access	Records are stored and retrieved by relative record number or by file address. Records occupy cells of equal length, and each cell is assigned a relative record number, which represents the cell's position relative to the beginning of the file.
Record File Address Access	When a record is accessed directly by its file address, the distinction is made by its unique location in the file; that is, its record file address (RFA).
Indexed Access	Indexed file records are stored and retrieved by a key in the data record. The desired records are usually accessed directly and then retrieved sequentially in sorted order using a key embedded in the record.

The record format is the way all records in a file appear physically on the recording surface of the storage medium. RMS supports four record formats as described below: 

Record Format	Description
Fixed length	All records are the same length.
Variable length	Records vary in length. Each record is prefixed with a count byte that contains the number of bytes in the record. The count byte may be either MSB- or LSB-formatted.
Variable record length with fixed-length control	Records do not have to be the same length, but each includes a fixed-length control field that precedes the variable-length data portion.
Stream	Records are delimited by special characters or character sequences called terminators. Records with stream format are interpreted as a continuous sequence, or stream, of bytes. The carriage return and the line feed characters are commonly used as terminators.