To demonstrate you can create entity relationship diagrams extend the EER as described in Basis.dia by modelling new requirements as follows:

a) The system has an online catalogue, which stores a reference to an album. An album can have a number of entries in the catalogue determined by the release date of the album (to account for re-releases). The catalogue also stores the price of each entry and the number in stock (available).

b) A buyer can place an order. We use the buyers code to uniquely identify the buyer with the order and so an entity for the buyer needs to be created (we also store their name).

c) A buyer can place any number of orders, each of which has an order number and a dispatch date. An order also composed of separate parts each of which referrers to a catalogue entry.

d) Create subclasses to extend Artist. Two different types of Artist exist: a Solo artist and a Group artist. A solo artist can be a member of more than one group and group is made up of one or more solo artists.

e) Extend Album thus: an album comes in one of three types Vinyl, Tape, and CD discriminated by v, t, and c respectively. A vinyl album can come in a number of colors, a CD album can have a number of different pc extras, and a tape can have only one label type.

f) Now explain the category relationships: supertypes and subtypes that you have just created.

g) Explain the relationship CreatedBy.

h) Explain the relationship GroupedOn.

i) Is it possible for many artists to appear on one album?

name date_from contact_ID ( telephone ) date_to 1 Contractinfo duration Manager I ManagedBy > Master Track EditedBy > Sound Engineer CreatedBy >> title OriginatesFrom> album_ID m Finished Track - Album version sequence final_duration released_title ) name date_from contact_ID ( telephone ) date_to 1 Contractinfo duration Manager I ManagedBy > Master Track EditedBy > Sound Engineer CreatedBy >> title OriginatesFrom> album_ID m Finished Track - Album version sequence final_duration released_title )