ClearCase is a Software Configuration Management System
from Rational Software, Inc.
It keeps track of which
versions of which files were used to build each release
of a software product and it helps organize the work of
groups of engineers.
10 Questions About ClearCase Answered by
- What is ClearCase and why would my company want it?
- So, is it a database? We already have Sybase, why do we need ClearCase?
- OK then, maybe I want a system like this, is ClearCase any different from the other SCM systems out there?
- It sounds fancy, but what I really need is a system that will save my engineers time. Will ClearCase save or cost time?
- We do parallel development right now -- we have copies of our product codeline owned by each group. It is very expensive for us to integrate the work across groups. Will ClearCase be any better?
- OK, lets say we bring in ClearCase... How long will it take before it is stable and useful?
- Our product takes a long time to build, so we want to do nightly builds and let the engineers use the results in the mornings, instead of every engineer doing their own builds. Can ClearCase do that?
- What are the risks of using ClearCase?
- We want to become ISO-9000 compliant, will ClearCase help us?
- I've heard that it can be hard to find infrastructure engineers. Why?
- What is ClearCase and why would my company want it?
ClearCase is a Software Configuration Management (SCM) system.
That means it keeps track of which versions of which files
were used for each release (even internal releases) and
also which combinations were used in builds (including engineer
builds, nightly and release builds). ClearCase also provides
a rich and robust set of tools to allow a company to craft their
engineering environment to their own requirements.
Your company would want ClearCase to help organize and address the
increasingly complex problem of release and build management. You'd
also want ClearCase to help you begin to replace your aging
software engineering infrastructure. ClearCase would replace large
portions of it with modern technology, allow much of the rest to
run unchanged, and make it easier to implement high quality replacements
for what remains and for new needs.
- So, is it a database? We already have Sybase, why do we
ClearCase contains a database, but it also contains many special
applications which are tailored to facilitate the tasks engineers
perform. SCM is a hard problem to solve well. The folks who created
ClearCase actually previously implemented a very respectable, highly
touted SCM system called DSEE, which ran on Apollo systems. ClearCase
picks up many of the strong points of DSEE, but brings them to most of
the modern development platforms, including NT. ClearCase isn't really
an expert system; however, some of its tools contain the expert
algorithms from highly experienced SCM System engineers.
You wouldn't want to have your own engineers try to implement an SCM
system for your company, because it would be a huge undertaking. The
effort is likely to produce a system with problems and limitations,
and those will interfere with engineering from then on. Many policies
will exist only to work around the limitations, and in the end,
the system will limit the options of the engineering staff. In short,
no money could possibly be saved by implementing your own SCM system,
even if you already have engineers, a database, and time.
- OK then, maybe I want a system like this, is ClearCase any
different from the other SCM systems out there?
Yes, ClearCase is fundamentally different. ClearCase becomes a part of
the operating system, so it has complete control over all access to files
it manages. This is necessary both for security and so
it can offer a transparent SCM service. You enter
structure which is managed by ClearCase, and you see files. Which
versions of those files you see is based on a set of rules and a
point in time (the current moment by default). You can back in time
and you see different versions of files. You can use different
rules and see different releases. All in the same directory structure,
which itself is managed by the system. The end result is that many
tools and techniques which worked in a previous SCM system (e.g. a
in-house-built one) continue to work under ClearCase.
Another reason transparency is important is because almost any tool
or program (e.g. web servers, desktop publishing systems,
compilers, etc.) run inside of a ClearCase managed directory structure
benefits from the rich SCM environment ClearCase offers. You don't have
to teach each new tool about how your SCM system works. That means
you can manage practically all your product-related files under the
same system. That way, when you look at a historical release, you
can easily get its documents, and other related files, knowing that
they all went together at that time. Other SCM systems don't offer
transparency through the operating system. They are applications,
and as such cannot exert the kind of control nor be privy to the
kind of information ClearCase has and needs to do the job well.
- It sounds fancy, but what I really need is a system that will save
my engineers time. Will ClearCase save or cost time?
At first, the transition to ClearCase will cost time, just as any shift
in infrastructure will. People will need to learn the new tools, and
ClearCase must be set-up on various computers and workstations. Large
installations must consider network issues to avoid unnecessary
Once implemented the ClearCase offers many opportunities to save time.
These include (at least):
- parallel development
- mostly-automated merging
- derived object sharing
- distributed builds
- fast, extensible database
If you use ClearCase exactly like your previous SCM system, you won't
get any of these benefits of these opportunities. If you really just
want something like SCCS, then SCCS is a better fit. But SCCS doesn't
scale to the size and complexity of modern products, organizations,
and development and release methodologies.
Using these capabilities in ClearCase can increase the complexity of
the engineering environment, but ClearCase provides the tools to
effectively cope with and manage that complexity. Frequently the
business needs of a company force its engineering organization to
undertake increasingly complex tasks. For example:
- fixes (or special combinations of fixes) for special customers
- movement of features from release to release
- beginning a new release before the previous one is completed
- more and more platforms
- more and more products
- more and more feature interactions
- demand for higher quality
- demand to accelerate schedules
There are few if any simple answers to these problems that organizations are
not already employing. To effectively cope, an organization needs
methods and tools which don't buckle under increasing complexity.
ClearCase is such a tool. Using techniques like branching and merging
an organization using ClearCase can perform even the most complex
Software engineering in a growing company is inherently increasingly
complex. Saving time means not only getting the same job done in
less time, but also minimizing the time required to cope with
increasing complexity. Failure to cope with complexity
successfully makes per-task time savings almost irrelevant.
So, yes, you can save time using ClearCase, and you can keep increasing
complexity from eating up all your time. You can also lose time if you use
or install ClearCase poorly. So, if you are serious about saving time
even in the face of increasing complexity, you are ready for ClearCase.
- We do parallel development right now -- we have copies of our
codeline owned by each group. It is very expensive for us to integrate
the work across groups. Will ClearCase be any better?
Yes. First, ClearCase doesn't depend on copies of the repository.
Instead, a branch for a file is created the first time someone in
group checks the file out. From then on, everyone in the group works
on the branch for that file. Files that were never checked out
have no group branch. So, small parallel projects might branch only
a few percent of the files, making them much easier to integrate with
the work of other groups. This sparse branching model is much more
efficient than copies of the repository.
ClearCase also provides excellent merge technology. ClearCase takes into
account previous merges and the physical geneology of files when merging.
It can automate many aspects of merging, and the entire merge in some
cases. Code conflicts must still be resolved by an engineer, as with
any automated merge tools.
The combination make parallel development (work on branches) both
practical and convenient.
- OK, lets say we bring in ClearCase... How long will it take
before it is stable and useful?
That depends on many factors, but you can expect at least a few months.
Many companies make the decision to buy ClearCase and then create
aggressive schedules for its implementation. This doesn't work for a
lot of reasons including:
- computer acquisition, installation and configuration takes a long
time at most companies
- network configuration takes a long time at most companies
- ClearCase codeline administrators need time to get up to speed
- engineers need time to learn the system
- engineering groups need to pick their own suitable windows in time
to change over to the new system
- some analysis must be performed and subsequent decisions made
to plan for growth and long term use of ClearCase.
- some analysis must be performed and subsequent policies established for how ClearCase is used and administered.
Pushing too aggressively can also burn out your ClearCase experts, who are
in tremendous demand in the industry right now, and are difficult to
So, go slowly and carefully. Give your engineering organization time to
make a reasonable transition. Improving software engineering infrastructure
is a long-term commitment, and takes time to implement well. Short-term
thinking can be disastrous in infrastructure, because the cost of rework
can be quite large. Do it as well the first time as possible.
- Our product takes a long time to build, so we want to do
and let the engineers use the results in the mornings, instead of every
engineer doing their own builds. Can ClearCase do that?
Yes, through the derived object sharing capability. ClearCase provides
a make-compatible build system called ClearMake. ClearMake can determine
that the derived object from one engineer or a nightly build depends upon
all the same versions of files as another engineer is using. When that is
the case, no compile is necessary, and the derived object is made available
to both. It just "winks into" the workspace as though a compile had
ClearCase takes into account the entire build command line, so objects
from other architectures or with different compilation options are not
- What are the risks of using ClearCase?
ClearCase operates over your internal LAN, and in multiple subnets if
you have them. There will be at least one computer whose failure shuts
down ClearCase for some segment of users. Also, the failure of certain
network equipment could make it seem that a critical host was down, having
the same effect.
In general, the repository is remarkably robust. So, even in the face
of an unstable computing and network environment, the mode of failure
is generally lost access, not corrupted data.
Companies with crumbling computing and network environments have the
most difficulty implementing ClearCase because it will make a bad
To use ClearCase well generally requires reconsideration of existing
policies and practices. This is a healthy step for any organization.
It is better to pare back policies at first and (re)establish the needed
ones over time. There is a risk that setting up too many policies in
ClearCase right at the start can slow the system down and make it less
robust. This can undermine confidence and enthusiasm in the system,
both of which are helpful for a successful transition.
- We want to become ISO-9000 compliant, will ClearCase help
ClearCase can help a lot. First, you can manage your ISO-9000 documents
under ClearCase. That provides both versioning of the files, but also
affords you the opportunity to easily limit who can change the documents.
ClearCase provides a rich set of tools for automating or enforcing
policies as needed. The ISO-9000 written policies can have a
real-world, demonstrable implementation which ensures that they are
ClearCase provides a flexible query tool for the production of reports
which monitor compliance with your policies (for example, to look for
check-ins which didn't receive a review).
- I've heard that it can be hard to find infrastructure engineers.
Historically, the software industry has placed a low value on software
engineering infrastructure. The tasks of creating and maintaining it
were often added onto an already full workload of a senior or staff
engineer with many other responsibilities.
As a result, few engineers ever had the opportunity to focus on
infrastructure -- there was no career path in most companies. Then in
about 1990, the industry began to wake up to the fact that quality,
meeting schedules, and even engineer morale depended upon a sound
software engineering infrastructure. Companies began to strive for
SEI level 2, and later ISO-9000 compliance. To remain competitive
they had to get more features out sooner and at a higher quality level
than their competitors. This in the face of increasing complexity.
So, many companies realized that their engineering infrastructure needed
a lot of work, and they began looking for suitable engineers. But there
aren't many (yet) because there was no career path until recently for
them. Since so many companies are interested in improving their
infrastructure, and there aren't enough people who know how to do it,
companies must often look within to find suitable engineers, or risk
hiring someone with the expectation that they will grow into the
job. I think more success is had with internal candidates because they
already know the culture and policies of the company, which are vital
to their ability to succeed in their new role. Such a position needs to
be made attractive -- remember, the message engineers have received for
a long time is: "do infrastructure work on your own time". It takes
some clear messages from the very top of the company to turn that kind
of attitude around and make an infrastructure position attractive enough
for someone to change their career path.