Design for Project C and use views for Projects A and B.

HTH
Jerry

The script below for a small experimental db models the above in a
normalized manner. The db allows each thing to have any number of
classifications and properties; each property can have any number of
values; and each value can have any number of types. Constraints (ie
which attributes are appropriate for a thing) aren't enforced by the db
and need to be implemented in user's code.

// Create items in directory to classify things.
(CREATE *project.item ~in = dir)
(CREATE *person.item ~in = dir)
(CREATE *email.item ~in = dir)
(CREATE *address.item ~in = dir)
(CREATE *gender.item ~in = dir)

// Create verb to relate person to project
(CREATE *member.cls = verb)

// Create projects A, B, C.
(CREATE *projectA.cls = project)
(CREATE *projectB.cls = project)
(CREATE *projectC.cls = project)

// Create projectA member with name and email.
(CREATE *.name = +john)
(CREATE john.cls = person)
(CREATE john.email = +"j@hot.com")
(CREATE projectA.member = john)

// Create projectB member with name, email and address.
(CREATE *.name = +mary)
(CREATE mary.cls = person)
(CREATE mary.email = +"m@hot.com")
(CREATE mary.address = +"123 main st")
(CREATE projectB.member = mary)

// Create projectC member with name, email, address and gender.
(CREATE *.name = +bob)
(CREATE bob.cls = person)
(CREATE bob.email = +"b@hot.com")
(CREATE bob.address = +"456 walnut st")
(CREATE bob.gender = +"male")
(CREATE projectC.member = bob)

// Find projects that has a member that is male.
// Finds projectC.
(SELECT %.member=(%.gender=male))