Rational ClearCase is a family of computer software tools that supports software configuration management SCM of source code and other software development assets. It also supports design-data management of electronic design artifacts, thus enabling hardware and software co-development. ClearCase includes revision control and forms the basis for configuration management at large and medium-sized businesses, accommodating projects with hundreds or thousands of developers.
It is developed by IBM. Both can be configured to support a wide variety of needs. ClearCase can accommodate large binary files, large numbers of files, and large repository sizes. It supports branching, labeling, and versioning of directories. In particular, it supports dynamic views which can show an arbitrary combination of local and remote files. ClearCase was developed by Atria Software and first released in  on Unix and later on Windows.
The Apollo Domain file system allowed special handler programs to intervene during file access. DSEE made use of this feature to invisibly substitute a versioned copy when a particular file was opened.
DSEE relied heavily on a file that described all the software modules and their dependencies. The file had to be generated manually, which was a major impediment to its use in large systems.
However, once generated, it enabled DSEE to calculate the optimum way to perform a build, re-using all modules that had previously been processed and whose version specifications matched the specifications for the build.
DSEE also introduced the "version spec," which was called a "thread. A major innovation was the use of build signatures and software release signatures in the thread. The items in a thread might thus be:. Threads were processed from top to bottom for each file.
A developer thread might have "reserved" at the top, followed by a labeled version. For a fix to an existing release, the thread would be "reserved", then the release signature. In the absence of the invisible file redirection of the Apollo Domain file system, ClearCase uses the virtual file system provided by the MVFS feature that is described below.
The "thread" concept corresponds to the dynamic view. Support for derived objects in a view is similar to DSEE's concept. On this layer, maintenance takes place using Raima tooling. Around this layer, a set of interfaces with accompanying tools are used to manage the physical database system, which requires specific Database administrator skills.
Before version 7 there was a web service by which users could access ClearCase via their browsers. A distinguishing feature of ClearCase is the MultiVersion File System MVFSa proprietary networked filesystem which can mount VOBs as a virtual file system through a dynamic viewselecting a consistent set of versions and MVFS - Many Very Fine Songs 95-99 the production of derived objects.
This was a departure from Romance (Extrait DUne Petite Musique De Nuit) - Albinoni*, Mozart*, Barber*, Tchaikowsky*, Bach* - repository-and-sandbox model because it enabled the early management of artifacts that is, before they are checked in and was not limited to the management of these first-order configuration items.
ClearCase also supports snapshot views, which are copies of repository data. As opposed to dynamic views, snapshot views are maintained on a local OS-specific file system and do not require network MVFS - Many Very Fine Songs 95-99. Instead, a snapshot view stores a copy of the VOB data locally on the user's computer. Snapshot views can be used while disconnected from the network and later synchronized with the VOB when a connection is reestablished.
From the perspective of the client computer, a ClearCase view appears to be just Tomorrow Says Goodbye (Demo) - Apple Orchard - Coffee Morning, 6AM (A Compilation, 2006-2013) file system.
New files and directories created in a ClearCase view are referred as "view-private" to indicate that they are specific to the view and not version-controlled. This feature allows build systems to operate on the same file system structure as the source code and ensures that each developer can build independently of one other.
At any time, a view-private object can be added to source control and become a versioned object, rendering it visible to other users. Developers Mutter - Rammstein - Mutter have one or more views at their disposal.
It is sometimes practical to share views between developers, but sharing branches is the more common practice. A branch hierarchy MVFS - Many Very Fine Songs 95-99 often useful: an entire development project can share a common development branch, while a smaller team can share a sub-branch, with each developer having his or her own private branch.
Whenever a change on a branch is deemed stable enough, it can be merged to the parent branch. Under base ClearCase, each view is controlled by its associated configuration specificationcommonly referred to as a config spec. This is a collection of rules stored internally in a text file, but compiled before use that specifies what element versions files or directories are to be displayed in a view.
To determine which version, if any, of an element should be visible, ClearCase traverses the configuration specification line-by-line from top to bottom, stopping when a match is found and ignoring any subsequent rules.
A configuration specification can also reference other configuration specifications by means of an 'include' statement. In the UCM management model, config specs do not need to be created or maintained manually: they are generated and maintained by ClearCase UCM operations. The networked filesystem provided by MVFS allows for build auditing. This allows ClearCase to produce a bill-of-materials which it calls a Configuration Record CR MVFS - Many Very Fine Songs 95-99 all builds and enable traceability for either software configuration management purposes or as part of a larger application Михаил Пляцковский - Дружба Начинается С Улыбки management process.
Build auditing is performed with command-line tools such as a built-in make tools omakeclearmake or by using the clearaudit command, which can invoke another build tool, such as Unix make 1.
The Versioned Object Base VOB that stores versions of file elements and directory elements also stores derived objects and metadata associated with these object types.
The bill-of-materials artifact produced as the result of build auditing is known as the Configuration Record. It contains:. The dependency information is stored in a configuration record that can be shown for each derived object.
The configuration record can be used to create another view that shows all files that have been previously read during the build time. The MVFS - Many Very Fine Songs 95-99 record can also be used to apply a label to the files and versions that were read during the build. The MVFS - Many Very Fine Songs 95-99 allows derived objects that were built in one dynamic view to be automatically "copied" to another dynamic view that requires "exactly the same" derived object.
Two derived objects are deemed to be "exactly same" if they have the same configuration record that is, bill of materials. The shareable derived objects are physically present in the VOB server, not in the views that reference them. This feature is called winking in derived objects and requires that the MVFS - Many Very Fine Songs 95-99 or omake tool is used for builds.
ClearCase dynamic views are slower than local filesystems, even with a good network infrastructure. Repeated subsequent builds may run faster, due to build avoidance that is enabled by ClearCase's make substitute. Because MVFS requires server access every time a file is accessed, the performance of the file system depends on server capacity. Originally, ClearCase supported only full "fat" clients running native on Unix and Windows.
It is based on Eclipse software and supplied in both fully packaged Eclipse versions, as a plugin-in for Eclipse, and for other environments such as Visual Studio. Each location site has its own copy replica of the VOB.
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