bdfm1m0xMessages (System Error, Online, Offline) and Master Glossary

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B+Tree index
A file structure where all data is contained in data blocks and a B+Tree indexes into the data blocks. The B+Tree, which consists of nodes, is maintained internally by the TPFDF product. The nodes consist of one root node, internal nodes, and leaf nodes. The root and internal nodes point to other nodes, and the leaf nodes point to data blocks. The B+Tree is dynamically balanced so that the B+Tree is of uniform depth. See also root node, internal node, and leaf node.

basic indexing
A method of creating TPFDF structures that include index and detail files.

block
A physical storage area used by the TPFDF product that contains a header, logical records (LRECs), and an optional trailer. (A block is the TPFDF term for a TPF or ALCS record.)

block header
The standard header in data blocks (records) that includes information such as the file ID, the record code check (RCC), data control, program name, and chaining address fields. The block header for TPFDF blocks includes all fields in the standard TPF and ALCS header plus additional fields used only for the TPFDF product.

block index support
A method that the TPFDF product uses to identify which logical records (LRECs) are contained in overflow blocks of a subfile. Block index support allows faster access to LRECs in overflow blocks. This support only works if the LRECs are organized UP (ascending) or DOWN (descending) in each subfile.

block trailer
An optional area located at the end of each TPFDF block that contains information about the block.