one doctor. This constraint needs to be described in the schema.There are two main types of structural relationship constraints on: cardinality ratio, and participation Q.105
Discuss the techniques for a hash file to expand and shrink dynamically. What are the advantages and disadvantages of each...
) of an entity type (student)
Relationships between data tables define cardinality when explaining how each table links to another.
In the relational model, tables can be related as any of: many-to-many, many-to-one (rev. one-to-many), or one-to-one. This is said to be the...
-recipe, or fixed-proportion) constraint. The formulette
might be better expressed: (1/ 7) X1 = (1/ 9) X2 . Here too, we suggest trying a numerical
example for X1 and see what that implies for X2.
“Sorties of type X1 must constitute at most 33% of all sorties of type X1, X2, and X3...
the designer should model a relationship as an associative entity type. 11. List the fourtypes of cardinalityconstraints, and draw an example of each. 12. Give an example, other than those described in this chapter, of a weak entity type. Why is it necessary to indicate an identifying relationship...
consider the following three type of constraints. First, the asset bounds constraint, i.e., the minimum and maximum proportions of each asset’ investment in the s portfolio. Second, the cardinalityconstraint, i.e., the desired number of assets in the portfolio.
Third, the group constraint and the...
to obtain the required information from my client. This questioning helped me understand how the client deals with customers and what product information he felt was important to provide to customers. Table 1 is an excerpt of the knowledge audit. In addition to past and future example, categories...
…………………….. |Pg.63 |
Whenever a sports day is held, there are a lot of data needed. For example, the personal data of students, data about the events (time, place and venue) and teachers’ job etc. All these data need to be...
Describe the cardinality and optionality of the relationships
Examine the constraints between participating entities.
Remove redundant relationships
Examine the ER model for redundant relationships.
ER modelling is an iterative process, so draw several versions, refining each one until you are happy with it. Note that there is no one right answer to the problem, but some solutions are better than others!...
, objects are qualified as one of three types: dimension, detail, or measure. Object type Description Parameters for analysis. Dimensions typically relate to a hierarchy such as geography, product, or time. For example. Last Name and City_Id Provide a description of a dimension, but are not the focus for...
such as counting, summing, averaging, sorting, grouping, cross-referencing, etc. Rather than have each computer application implement these from scratch, they can rely on the DBMS to supply such calculations.
• Change and access logging: Often one wants to know who accessed what attributes, what was...
. For example, MANAGES and WORKS_FOR are distinct relationships between EMPLOYEE and DEPARTMENT, but with different meanings and different relationship instances.
Constraints on Relationships
Constraints on Relationship Types (Also known as ratio constraints)
• Maximum Cardinality...
representation provides a better means of expressing referential integrity constraints.
A schema for four relations at Pine Valley Furniture Company
It is a good idea to create an instance of your relational schema with sample data for four reasons: a) The sample data allow you...
later in the next section. If one CUSTOMER can be related to only one ACCOUNT and one ACCOUNT can be related to only a single CUSTOMER, the cardinality of the CUSTOMER-ACCOUNT relationship is one-to-one (1:1). [Note that eachcardinalitytype is followed by a shorthand notation in parentheses.] If an...
their Sup. It makes it unnecessary to include Sup Att redundantly with Sub. Types of Bus rules in EER: The terms, relationship constraints, & Sup/Sub relationships. Sub discriminator purpose: to determine the target Sub for each instance of a Sup. Utility of packaged D model: useful when one can...
simultaneous relationship among the instance of 3 entity types.
A cardinalityconstraint is a constraint that specifies is constraints that specify the number of...
—cardinalities, existence dependencies, and keys.
Cardinalities. Cardinalities can express the number of entities to which another entity set can be associated via a relationship set. There can be fourtypes of relationships among two or more entities—one-to-one, one-to-many, many-to-one, and many-to-many.
(ER) diagram for the video company that identifies:
i) The entity types of the video rental company.
ii) The relationship types between the entity types.
iii) The cardinality and participation constraints for each relationship.
iv) The attributes of each entity and the relationship types.
candidate relations derived from the ER
Data Dictionary entries from the candidate relations.
Clearly identify the table name, attribute names, and attribute data types. Indicate the primary keys and/or foreign keys.
Carefully read all the details for each part of the task, which...
and its two relationships to Guest and Account could be “collapsed” into a composite, more abstract relationship linking Guest and Account directly. That composite relationship should be of type association with the cardinality “0..1”. This example shows a case where knowledge about the semantic...
, each of the entities including the Associate
entities is transformed into a table. The attributes (fields) of each of the entities for the
ERD shown in Figure 1 are as follows.
SNO NAME DATA TYPE WIDTH CONSTRAINTS
1 USERID INT 10 PRIMARY KEY
2 USERNAME CHAR 20
3 PASSWORD CHAR...