Different  architectures, which are used in SCM Programs

File server architecture. (MKS,PVCS,VSS)

In these  systems  information is accessible from all computers with client program
without special server program.

The main pluses:

 - user has a full control of all operation, he/she has possibility manually change something in archives, if he knows structure of archives. He can repair damaged files, to change configuration files for including or removing different components, to move archives from one place to another.

The main problems :

- Simultaneous access to archives or configuration files. For example -when  two or more clients want to do operation with the same  file or folder ( checkin, check out etc.) The same problem - when one user want to add files to project , which in the same time is open to other clients the  For resolving of this problem usually special mechanism of locking is needed. In most of the system it is a various types of  semaphores - native for operation system or special for product. Semaphore - it is a special file which created for “closing” access to file and automatically deleted after ending opeartion. For example in PVCS when you want to do check in or checkout opeartion for file with name xxx.cpv, in directory where this file is placed will be created semaphore   file with name xxx.$$$ with size 0 byte. After finishing operation file will be deleted automatically.

- usually information is placed right in file system, and occasionally may be destroyed or damaged.

- during any operation (label, lock etc. ) only power of client computer is used, server is used only for file storage. For big projrct with 1000+ files it is a problem.

- it is very hard (and even dangerous) to operate with internet, because you can give to user access to your file system, and all user should have installed client program.

Client server.

In this architecture always exist special server program, which is used for access to data.

The main pluses :

- for all operation power of server computer is used.  Usually server has more CPU, than client computer .

- access to all information only from one server  program. In this case all problems of security, simultaneous access etc. have a full built in decision.

- all information is closed from user ( usually in databases) and it is not so simply to damage it.

- access from Internet may be organized very easy. It is not needing to use special client program, because in this case also work server program

The main minus:

 - user cannot interrupt to process,  it is more “closed” systems, then file server.  

Daemon structure.

It this structure on each computer should work two programs - client of SCM and also special program ( demon) which used for link between computers. Link organized with usage TCP/IP address.

 Usually special program like server should be installed on server computer. In TrueChange program we have even two server programs - “License server program” and “Repository server program”.

In this case system will be “platform independent”, because on each station will work demon program which is matching to its platform, and link between computers -only by IP.

Main plus of this type of SCM product - it  can work on distributed network - with PC, UNIX, VMS and MVS systems as client, and repository may be placed on any type of computers