type_object

Prototype for data items stored in a VOB

APPLICABILITY

ClearCase (data structure), Attache (data structure)

DESCRIPTION

A type object is a prototype for one or more data items stored in a VOB database. A user creates the data items by entering commands that create instances of the type object.

For example, to attach the version label BASELEVEL_4.2 to the current versions of a set of source files:

• Verify that there exists a type object that defines the version label. Or, you create such a label type object (mklbtype command).
• Create the individual version labels as instances of the BASELEVEL_4.2 label type object (mklabel command).

NOTE: The phrase "type object" is sometimes shortened to "type" in ClearCase documentation.

INSTANCES OF TYPE OBJECTS

Creating an instance of a type object is not a copy operation. Rather, the instance is a reference to the type object. In the example above, attaching version label BASELEVEL_4.2 to a particular version does not make a copy of the BASELEVEL_4.2 type object. Instead, it establishes a connection between the version object and the label type object.

This scheme makes it easy to administer type objects and their instances. For example, renaming the label type object from BASELEVEL_4.2 to BL4.2 renames all its existing instances.

NOTE: Creating an instance does not make a copy of the type object, but in certain cases it does create a new object. For example, the mkbranch command creates a new branch object and creates a reference connecting the new branch object to an existing branch type object. See PREDEFINED AND USER-DEFINED TYPE OBJECTS for information on which types are associated with objects.

KINDS OF TYPE OBJECTS

To support different kinds of data items (version labels, attributes, branches, hyperlinks, and so on), there are different kinds of type objects:

Attribute type (mnemonic: attype)

Instances are attributes. The following kinds of objects can have one or more attributes attached to them: elements, branches, versions, hyperlinks, VOBs, VOB replicas, any type object.

Branch type (mnemonic: brtype)

Instances are branches, which are objects in their own right.

Element type (mnemonic: eltype)

Instances are elements, which are objects in their own right.

Hyperlink type (mnemonic: hltype)

Instances are hyperlinks, which are objects in their own right.

Label type (mnemonic: lbtype)

Instances are version labels. One or more version labels can be attached to any version object.

Trigger type (mnemonic: trtype)

Instances are triggers.

The mnemonics listed above are useful as object-selector prefixes in ClearCase product family commands. By default, many commands consider an unprefixed name to be a reference to a file system object, typically a version of an element:

cmd-context describe hoople
(describe the file named `hoople' in the current working directory)

cmd-context describe brtype:hoople
(describe the branch type object named `hoople')

PREDEFINED AND USER-DEFINED TYPE OBJECTS

Each VOB is created with a set of predefined type objects. Users can create additional type objects.

• Predefined element types:

  file_system_object (internal only; cannot be used in a mkelem command)
  directory
  file
  binary_delta_file
  compressed_file
  text_file
  compressed_text_file

• Predefined branch type: main
• Predefined label types:

  CHECKEDOUT
  LATEST

• Predefined attribute types:

  HlinkFromText
  HlinkToText

• Predefined hyperlink types:

  AdminVOB
  GlobalDefinition
  Merge
  RelocationVOB

SCOPE OF TYPE OBJECTS

Each VOB has its own set of type objects, for use in creating instances of the types in that particular VOB. For example, you can attach RLS7.0 version labels within a particular VOB only if label type RLS7.0 already exists in that VOB. Exception: The global type object facility creates type objects on demand by copying them from a networwide repository. See GLOBAL TYPES AND ADMINISTRATIVE VOBS for details.

GLOBAL TYPES AND ADMINISTRATIVE VOBS

You can use the global type facility to effectively increase the scope of a type object from a single VOB to a group of VOBs-perhaps all the VOBs in your local area network. You can create any number of global type objects in one or more central administrative VOBs.

For more information about using global types, see Administering ClearCase.

OPERATIONS ON TYPE OBJECTS

The following commands operate on type objects. For more information about the commands, see ClearCase Reference Manual. For more information about how these commands work with global types, see Administering ClearCase.

SEE ALSO

describe, mk**type, rename, rmtype