tailieunhanh - Lecture Database Systems - Lecture 23

This chapter covers advanced data types and new applications, including temporal datababases, spatial and geographic databases, multimedia databases, and mobility and personal databases. This chapter is suited as a means to lay the groundwork for an advanced course. Some of the material, such as temporal and spatial data types, may be suitable for self-study in a first course. | CSC271 Database Systems Lecture # 23 Summary: Previous Lecture Database design using ER modeling Concepts of ER model Entities Relationships Attributes Classification of Entity Types The entity types can classified into Strong entity type Weak entity type Strong Entity Type Strong entity type An entity type that is not existence-dependent on some other entity type . Staff, Branch, PropertyForRent, Client etc. A characteristic of a strong entity type is that each entity occurrence is uniquely identifiable using the primary key attribute(s) of that entity type For example, we can uniquely identify each member of staff using the staffNo attribute, which is the primary key for the Staff entity type Sometimes referred to as parent, owner, or dominant entities Weak Entity Type Weak entity type An entity type that is existence-dependent on some other entity type . Preference etc. A characteristic of a weak entity is that each entity occurrence cannot be uniquely identified using only the attributes associated with that entity type For example, note that there is no primary key for the Preference entity, means that we cannot identify each occurrence of the Preference entity type using only the attributes of this entity Sometimes referred to as child, dependent, or subordinate entities Example: Strong/Weak Entities Attributes on Relationships Attributes can also be assigned to relationships For example, consider the relationship Advertises, which associates the Newspaper and PropertyForRent entity types To record the date the property was advertised and the cost, we associate this information with the Advertises relationship as attributes called dateAdvert and cost, rather than with the Newspaper or the PropertyForRent entities Attributes on Relationships Diagrammatic Representation Attributes on relationship We represent attributes associated with a relationship type using the same symbol as an entity type However, to distinguish between a relationship with an . | CSC271 Database Systems Lecture # 23 Summary: Previous Lecture Database design using ER modeling Concepts of ER model Entities Relationships Attributes Classification of Entity Types The entity types can classified into Strong entity type Weak entity type Strong Entity Type Strong entity type An entity type that is not existence-dependent on some other entity type . Staff, Branch, PropertyForRent, Client etc. A characteristic of a strong entity type is that each entity occurrence is uniquely identifiable using the primary key attribute(s) of that entity type For example, we can uniquely identify each member of staff using the staffNo attribute, which is the primary key for the Staff entity type Sometimes referred to as parent, owner, or dominant entities Weak Entity Type Weak entity type An entity type that is existence-dependent on some other entity type . Preference etc. A characteristic of a weak entity is that each entity occurrence cannot be uniquely identified using only the