Zhengqi Li Yan Li Quiz Presentation 1 When converting a narrative requirements document into an ERD which of the following would potentially be converted into an entity type a Things ID: 261981
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Slide1
Group16
Zhengqi
Li
Yan Li
Quiz PresentationSlide2
1. When converting a narrative requirements document into an ERD, which of
the following would potentially be converted into an entity type: a. Things b. Places c. Events d. All of the above
Answer:D
Explanation: In a narrative, you should look for nouns representing people, things, places ,and events as potential entity types.Slide3
2. When converting a narrative requirements document into an ERD, which of
the following would potentially be converted into relationship type: a. Nouns b. Verbs and prepositions c. Adjectives d. Adverbs
Answer: B
Explanation: Relationships often appear as verbs and prepositions connecting nouns previously identified as entity types. For example, Student enroll in courses each semester indicates a relationship between students and courses Slide4
3. When converting a narrative requirements document into an ERD,
a. You can derive relationships but not cardinalities from the narrative b. You can derive cardinalities but not relationships from the narratives c. You can usually derive both relationships and cardinalities from the narratives, but sometimes they are incomplete d. None of the above
Answer: C
Explanation: In the narratives, you can find relationships through verbs appearing in the sentences. For relationship cardinality you should look at the number of nouns along with other words that indicate cardinality. You should look for singular or plural designation of nouns to decide the maximum cardinality and you should also look for optional or required language in sentences in order to determine the minimum cardinality. However, it is common to see that there is no narrative that states some cardinality(max or min) of one relationship, which will cause incomplete construction. At this time, maybe you should use default value such as mandatory for minimum cardinality. Slide5
4. In data modeling,
a. More than one alternatives may exist for a user requirement b. Additional information from user is usually needed in order to evaluate alternatives c. The process if usually iterative or repetitive d. All of the above
Answer: D
Explanation: When designing a database, you should carefully explore alternative designs since all of the transformations in the textbook is used to consider alternative designs such as expanding attribute and adding history. The process may be iterative or repetitive because in that way can you make sure this ERD is the most optimal one in the data modeling process. Your data model is often not complete without adequate design documentation and careful consideration of design errors, thus you should write documentation which indicate the lack of information needed and extra information should be given. Slide6
5. Redundant relationship in a database design:
a. Can be derived from other relationship b. Cannot be identified by reviewing the ERD c. Should always be removed from the database design d. None of the above
Answer: A
Explanation: Cycles in ERD may indicate redundant relationships. A cycle involves a collection of relationships arranged in a loop starting and ending with the same entity type. In a cycle, a relationship is redundant if it can be derived from other relationships. If you find cycles in an ERD when you review, you should be aware that there may exist a redundant relationship. However, you should take care when removing redundant relationships since removing a necessary relationship is a more serious error than retaining a redundant relationship. Therefore, when in doubt, you should retain the relationship.Slide7
Discussion Questions
6. How can you reduce the number of relationships in an initial ERD?Answer: In most situation, it is possible to reduce the number of relationships in an initial ERD since there ma be several design error in the initial ERD. The most common error is redundant relation due to cycles in an ERD. The resolution is that you should examine each relationship cycle to see if a relationship can be derived from other relationships and also you should know what will happen when removing redundant relationships since, sometimes, when you remove an important relationship in a cycle, this action will possibly lead to more serious error in the future. In some other situations, you may overuse M-way associative entity types since M-way relationships are not common, and you may reduce the number of relationships in an initial ERD by transforming a M-way relationship to multiple binary relationships. For example, in Employee, Skills, Project M-way relationship, there are three relationships. Nevertheless, you only have two relationships when you transform it to the binary relationship.