Constraint Sets

Every application needs a specific set of file structures, and any real system is likely to support only a limited range of file types, with restrictions on the ways you can modify files. Constraint sets express these limitations by restricting the following items.

Range of allowable file structures
Ways in which basic access actions can modify the structure

Constraint sets restrict (reduce) the file model. These sets help you efficiently model the type of file you are accessing.

The constraints sets supported by HP-UX FTAM are Unstructured and Sequential Flat.

Unstructured	Single, un-named data unit
Sequential Flat	Series of un-named data units

Each constraint set consists of the following items.

A statement of the intended field of application
A constraint set descriptor for reference in documentation
Constraint set identifier for reference in the FTAM protocol
Constraints on the node names
Set of valid file access actions
Qualified actions when writing to the file
Set of file access contexts in which the file can be read
State of the file when created
FADU located immediately after the file is opened
Definitions of "beginning of file" and "end of file"
Manner in which you read from or write to the whole file
General constraints on how you can modify the structure
Special semantics of specific file access actions
Allowable FADU identity forms for each of the file access actions

Access Contexts

Each constraint set contains a list of available access contexts which allow you to further restrict the file structure view during read operations. The Access Contexts are Unstructured All Data Units (UA) and Flat All Data Units (FA).

For FTAM-1, FTAM-3, and INTAP-1, only the UA access context is available. For FTAM-2, both UA and FA are available. If you use the UA access context when transferring FTAM-2 files, the file simplifies to an FTAM-1 file; the node descriptor information does not transfer.




	NOTE: Refer to the "FTAM Data Structures" chapter for detailed information on setting access contexts using the Ft_access_context structure.

Unstructured All (UA)	FT_UNSTRUCTURED_ALL_DATA_UNITS Only the data elements in the data unit (from the addressed FADU) transfer.
Flat All (FA)	FT_FLAT_ALL_DATA_UNITS Node descriptor information and data elements from the data unit (from the addressed FADU) transfer in the order that they are stored.

Unstructured Constraint Set

The unstructured constraint set applies to files that you can transfer or access in whole, or extend; partial access is not available.

Refer to the following list for applicable basic constraints.

Constraint Set Name	Unstructured
Constraint Set Identifier	ISO Standard 8571 constraint-set (4) unstructured (1) (ASN.1 syntax for an identifier)
Node Names	None
Available File Access Actions	FT_FA_ERASE FT_FA_EXTEND FT_FA_READ FT_FA_REPLACE
Qualified Actions	None
Available Access Contexts	FT_UNSTRUCTURED_ALL_DATA_UNITS (UA)
Creation State	Root node with an empty data unit
Location After Open	FT_FIRST
Beginning of File	Not applicable
End of File	Not applicable
Read Whole File	Read in access context UA with a FADU identity of FT_FIRST
Write Whole File	Transfer a single data unit (without a node descriptor) with a FADU identity of FT_FIRST and an FT_FA_REPLACE file access action

Additional constraints on the Unstructured constraint set are as follows.

Structural Constraints	All actions in the unstructured constraint set result in a structure with a root node that has a data unit (although this data unit may be empty).
Action Constraints	The FT_FA_ERASE action yields a root node with an empty data unit.
Identity Constraints	The FADU identity is always FT_FIRST. Use this form of FADU identity with all permitted file actions.

Sequential Flat Constraint Set

The Sequential Flat constraint set applies to files that are structured into a sequence of individual FADUs. You can access specific FADUs in the files by specifying their individual position in the sequence. Refer to the following list for applicable basic constraints.

Constraint Set Name	Sequential Flat
Constraint Set Identifier	ISO Standard 8571 constraint-set (4) sequential-flat (2) (ASN.1 syntax for an identifier)
Node Names	None
File Access Actions	FT_FA_ERASE FT_FA_LOCATE FT_FA_INSERT FT_FA_READ
Qualified Actions	None
Available Access Contexts	FT_FLAT_ALL_DATA_UNITS (FA) FT_UNSTRUCTURED_ALL_DATA_UNITS (UA)
Creation State	Root node without an associated data unit
Location After Open	Root node
Beginning of File	Root node
End of File	No node selected. FT_PREVIOUS gives last node in sequence; FT_CURRENT and FT_NEXT give an error
Read Whole File	Read in access context FA or UA with FADU identity of FT_BEGIN
Write Whole File	Transfer the series of leaf FADUs which would be generated by reading the whole file in access context FA; perform the transfer with a FADU identity of FT_END and an FT_FA_INSERT file access action

Additional constraints on the Sequential Flat constraint set are as follows:

Structural Constraints	The root node does not have an associated data unit. All children of the root node are leaf nodes and have an associated data unit. All arcs from the root node are of length one.
Action Constraints	You can use FT_FA_INSERT only at the end of a file, with FADU identity set to FT_END. The location following an FT_FA_INSERT action is FT_END. You can erase only at the root node to empty the file, with FADU identity set to FT_BEGIN. The result is a solitary root node without an associated data unit.
Identity Constraints	The FADU identity associated with the file action is FT_BEGIN, FT_END, FT_FIRST, or FT_NEXT. The allowable actions are as follows.

FT_FA_LOCATE	Actions are valid for each FADU identity on the whole file and on all leaf nodes.
FT_FA_READ	Actions are valid for the whole file at FT_BEGIN. Actions are valid for leaf nodes at FT_FIRST and FT_NEXT. Actions are not valid at FT_END.
FT_FA_INSERT	Actions are valid on the leaf node with the FT_END FADU identity.
FT_FA_ERASE	Actions are valid on the whole file only with the FT_BEGIN FADU identity.

Constraint Sets

Technical documentation

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Access Contexts

Unstructured Constraint Set

Sequential Flat Constraint Set