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Task analysis
Domain analysis
Of the real people/things, there are card signers, receivers, and owners. Owners are signers, because they sign cards too. Card signers may or may not have an account, similar to a Doodle poll where participants may simply only have a link to participate, but not necessarily an account. Participants without an account can only add a message, but to edit or remove their message, they must have an account.
Participants, with or without accounts will, have a participation link to to sign the card.
Accounts have a username, an email address, and a password. Accounts may create and administer their own e-cards, or create, edit, or remove (their own) messages on e-cards they have access to. An account has a list of e-cards they own (spear-heading) and a list of e-cards they are participating in.
E-cards have receiver links to send to the card's receiver, who will view the card. E-cards have a participation link, and messages that participants create and edit. Messages will contain any number of multimedia objects such as text, graphics, audio, and video.