I am pretty new to Hyper Ledger Composer. I understand the way it works.But my interest is to build a blockchain application for digital identity management.I have seen that Hyper Ledger is coming up with Indy project, but I wanna start things with the composer.
Not sure what the context of this question is - outnumbered by what ? In the context of your topic heading ; self-sovereign ID is a digital identification that can use 'consolidated bits of information' about the student and could be stored as a means of establishing the true identity captured in your model - in Composer, an identity that is transacting (creating, updating, querying) is known because it is registered on the business network, so as to access it in the first place (Certificate Authorities from 'whichever organisation' that's on that permissioned blockchain network, issues digital certificates for the transacting identities, in their own organisation/institution - they then connect to the network using that identity, obviously organisations will know who it is issued to).
See Difference between hyperledger composer and hyperledger fabric? and What are the functional differences between Fabric Javascript SDK and Hyperledger Composer? - also you see an introduction here -> https://hyperledger.github.io/composer/next/introduction/introduction.html
CGPA meaning : the average of grade points obtained in all the subjects ? Normally you wouldn't store sensitive information on a blockchain that's shared with other institutions, ie something like a StudentID / Surname might suffice? The records are the 'assets' and obviously the student is the participant in your model business network (simplistic). You can see more on sample business networks, with sample models and sample transaction code and ACLs here -> https://github.com/hyperledger/composer-sample-networks/tree/master/packages