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What do these access path terms mean?

The terms access paths, file indexes, and logical files are thrown around a lot and sometimes used interchangeably. What is the difference, and what exactly does each refer to in OS/400?

Physical File: The description and location of the data to be contained in a file. This description contains the record and field definitions as well as the access path by key and/or relative record access to the physical data located on the system.

Access Path: The stream that is created by OS/400, which defines the path to the physical data to allow the operating system to retrieve the requested records in the order and selection defined by the file being used. There is at least one access path for each physical file on the system. Logical files may also use the same access path, or create a new one based on the requirements of that logical.

File Index and Logical: A file index and a logical are usually the same term. A logical file is the description of what fields, concatenation and/or sub stringing of physical file fields), sorting (Indexing), selection and/or omission to the physical data. This is used by the system to access the data contained in the physical file in the order (index) and only allowing access to the fields defined (if omitted, all fields are accessible), and the order in which to retrieve any records that pass a selection or omission test, building of concatenated field and substrings of physical file fields.

Short version:

Physical file: Actual data, and optional keys by fields.

Logical file: Logical defined fields (or all), optional sorting key (index), select/omit, concatenation, substring.
Access path: The way the system finds the physical data.


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