5.1-Explain how entities are transformed into tables? 5.2-Explain how attributes

Question

5.1-Explain how entities are transformed into tables?

5.2-Explain how attributes are transformed into columns. What column properties do you take into account when making the transformation?

5.7-Explain how the representation of weak entities differs from the representation of strong entities ?

5.9-List the three types of binary relationship and give the example of each .do not use the examples given in the text ?

5.10-Define the term foreign key and give an example ?

5.14-Define the term parent and child as they apply to tables in database design and give an example of each ?

5.18-For a 1:N relationship ,explain why you must place the key of the parent table in the child table rather than place the key of the child table in the parent table ?

5.21- Explain the meaning of the term intersection table ?

Explanation / Answer

5.1

Entities can be transformed directly into SQL tables with all attributes mapped one-to-one to table attributes.Tables representing entities that are child of a parent-child relationship must also include as a foreign key,the primary key of the parent entity.A many-to-many relationship is transformed into a table that contains the primary keys of the associated entities as its composite primary key;the components of that key are laso designated as foreign keys in SQL. A ternary or higher level n-ary relationships are transformed into a table that contains the primary keys of the asociated entities;these keys are designated as foreign keys in SQL

5.2

Each attribute in an entity becomes a column in the corresponding table. The column properties are the same as discussed in the discussion of attributes. These include data type, null status, default values, and any constraints on the values.

5.7

A referential integrity constraint will be generated and a cascading deletions rule set up so that when the parent is deleted all dependent weak entities are also deleted. If the weak entity is ID-dependent, then the key of the relation upon which it depends will need to be added to the relation

5.9

In a marina: 1:1, BOAT to SLIP; 1:N, BOAT to RENTAL-CHARGE; N:M, BOAT to OWNER

5.10

A foreign key is an attribute that is a key of a different relation. SALES-ORDER(OrderNumber, OrderDate, SalespersonNumber, . . . ) SalespersonNumber is a foreign key (assuming there is a SALESPERSON table with SalespersonNumber as its key).

5.14

A parent is a row on the one side of a 1:N relationship. A child is a row on the many side of a 1:N relationship. Say DEPARTMENT and EMPLOYEE have a 1:N relationship, a row of DEPARTMENT is a parent and rows of EMPLOYEE that pertain to that department are children.

5.18

Not enough room. Can only have one value per cell in the relational model.

5.21

An intersection table implements a many-to-many relationship between two business components.A many-to-many relationship is one in which there is a one-to-many relationship from either direction. For example, there is a many-to-many relationship between Opportunities and Contacts. One Opportunity can be associated with many Contact people, and one Contact person can be associated with many Opportunities. Two different views can appear (in different business objects) which associate the two business components in opposite ways,

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