Version Control System: For my Ninth Grader - Part 1
Version Control System: For my Ninth Grader - Part 2
Day 3
Teacher: During our previous discussions we concluded that
no single approach is suitable for large scale collaboration. If we combine
multiple approaches then automation is require to derive substantial benefits.
So let us list what we need from a system which can facilitate large scale
collaboration:
- Single person should be able to work on a
document at a given point of time OR/AND multiple persons should be able to
work on a same document simultaneously
- Each individual should be able work on his copy
of document on his computer without need of connection to common computer.
- Each individual’s work should be traceable
- History of document should be constructable
- Documents should be protected against vandalism
- Individual contributor should be able to comment
about his work, so one can understand about his work without reading whole
document.
Let us build our understanding on the requirements of the proposed
system.
First requirement is full of contraction and made up of two
parts. Part One: Single
person should be able to work on a document at a given point of time.
This statement is straight forward. It simply says that on a given document at
a given point of time only one person should be able to work even that document
is available to multiple persons. Now,
how to achieve this? Very simple, make a
user interface (web page or some other software) which allow to mark a document
stating that this document has been checked out (remember in library you check
out a book) by Mr. X and do not allow anybody else to change the document till
Mr. X check in (again think of library) the document. In, library once a book
is checked out, book is not available on the book shelf in our proposed system
document is available but read only. If someone who has not checked out the
document and try to over write, should not be allowed to do so. Now Part Two: Multiple persons should be able to work on a same document
simultaneously. This requirement is in direct contrast to Part one. So,
what to do? What about a switch which can be flipped. If switch is in position
A, proposed system should behave to fulfill Part One requirement and if switch
is in position B then allow user to perform as stated by Part Two. Who has
control of this magic switch? Certainly not all users, only few privileged. We
call them Administrators. Part Two
requirement poses its own challenges. Think about following scenario:
There is a document (doc_under_test.doc) which is under
control of proposed system and Administrator is keeping the magic switch at
position B. At Oct 1, 2012 8.00 AM, Mr. X has checked out the document and
start working on it. While Mr. X is making changes to document, Mr. Y also came
in (at Oct 1, 2012 9.00 AM) and checked out the document and start working over
it. So, on same document two persons are working independently and not aware
what other one is doing with the document. At Oct 1, 2012 1.00 PM, Mr. Y checks
in his work. Everything is fine till this time. At Oct 1, 2012 3.00 PM Mr. X
checks in his document. After check in by Mr. X, work of Mr. Y is lost. How to resolve this challenge?
When Mr. X was checking in his document, flash a warning,
stating that the last time when you checked out the document and till now
document has changed, to avoid potential loss of work, find out the difference,
accept or reject the changes and then check in. Essentially human intervention
is required.
The second requirement of “each individual should be able
work on his copy of document on his computer without need of connection to
common computer” is pretty straight forward. Keep all documents on a common
computer and allow users to download the documents on their local computers.
The common computer can be called server
(one who serves) and a computer on which document is downloaded is called client (one who asks for service). This
technique will ensure that too many persons are not connected to server and
also each person can work on document without need to continuous (persisted)
connection to server.
The third requirement of traceability is also easy to
achieve. Not everyone is allowed to access the proposed system. Those who are
allowed should have some kind of user name and password to access documents. So
be in touch with your administrator to get user name and password. Whenever
someone checks out or checks in a document, log his user name. This will allow tracing,
who has interacted with system at what time.
The third requirement simply facilitates to find out that
who has interacted with system at what time but does not allow keeping record
of changes in document. So proposed system should keep copies of document with
each check in and correlate those copies back to users. To make easier for users,
show latest copy to users by default. So,
fourth requirement is fulfilled.
Since any interaction with document is traced to a single
user, chances of vandalism are greatly reduced. Who want to be caught!
The sixth requirement states about a desire also a good
practice. How to achieve it! Computer cannot figure out what is the description
of work a user has carried out. But proposed system can provide place holder
where a user can write a brief description of his work. Those who are
interested will read it. Think of Mr. X in Part Two of requirement one.
Students: Wow. Almost
all requirements are fulfilled.
Yash: Does system you
explained exist?
Teacher: Yes. It is called Version control system. It also has more fancy names such as Revision control system, source control system, and few more.
So using version control system vast number of people work
on projects, who are located in various countries and do not know each other.
That’s the beauty of version control systems.
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