Today we will continue our discussion on DBPowder. We will look into the conceptual model introduced by this framework. This paper proposes the following data models:
1) Object Model : This object is based on the subset of ODMG 3.0 standard, with some Java-based extensions. An object is called persistent if all property values are saved into the storage in order they may be retrieved later. Let us take an example with a class User that has an attribute user_name and has a relationship register to another class Register. The Register class also has a relationship user to the class User. Therefore the two classes have a bidirectional relationship. The cardinality is 1:n A class AdmUser is a sub class of the class User and the class User has a superclass of AdmUser and a class GuestUser
2) RelationalModel: The relational model has a table user and an attribute user_name and primary key user_id. A table register has a foreign key user_id to the table user.
3) EER model in DBPowder : The EER model describes the primitives such as attributes, entity, relationship, connectivity etc. The notations used are : e defines a fact, e has one or more attributes A1, A2 .. An. Entity E comprises of a set of facts | the entire attributes. Relationships are expressed as connectivity which represents cardinality.The relationship among three or more entities is described by another entity E' and connecting E' to each of the entities E1, E2, E3.
In the example taken earlier an entity user p has an attribute user_name q and a relationship r to an entity register. r has a connectivity 1:n. For entity user, the occurrence of entity register is mandatory , a constraint represented by s. The entities of user, adm_user and guest_user form a hierarchy with user as the base. Thus the EER can be used to generate both the relational tables as well as the simple correspondences.
1) Object Model : This object is based on the subset of ODMG 3.0 standard, with some Java-based extensions. An object is called persistent if all property values are saved into the storage in order they may be retrieved later. Let us take an example with a class User that has an attribute user_name and has a relationship register to another class Register. The Register class also has a relationship user to the class User. Therefore the two classes have a bidirectional relationship. The cardinality is 1:n A class AdmUser is a sub class of the class User and the class User has a superclass of AdmUser and a class GuestUser
2) RelationalModel: The relational model has a table user and an attribute user_name and primary key user_id. A table register has a foreign key user_id to the table user.
3) EER model in DBPowder : The EER model describes the primitives such as attributes, entity, relationship, connectivity etc. The notations used are : e defines a fact, e has one or more attributes A1, A2 .. An. Entity E comprises of a set of facts | the entire attributes. Relationships are expressed as connectivity which represents cardinality.The relationship among three or more entities is described by another entity E' and connecting E' to each of the entities E1, E2, E3.
In the example taken earlier an entity user p has an attribute user_name q and a relationship r to an entity register. r has a connectivity 1:n. For entity user, the occurrence of entity register is mandatory , a constraint represented by s. The entities of user, adm_user and guest_user form a hierarchy with user as the base. Thus the EER can be used to generate both the relational tables as well as the simple correspondences.
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