64 Part I EXAM PREPARATION Designing a good
64 Part I EXAM PREPARATION Designing a good database at this stage still does not require you to acquire the knowledge of how databases are implemented in SQL Server; rather it depends on how well you can comprehend a given scenario and its elements. The next section takes a look at entity composition and the defining of attributes. Defining Attributes Identifying attributes is the next step in ensuring a successful data modeling process, and moreover is a part of the Microsoft exam objectives for this chapter, defining entity composition, and the sub- objective, specify entity attributes. Attributes are characteristics or properties defined within a single entity, and they correspond to real-world properties of a place, thing, or concept. An attribute candidate is usually found by examining sentences in the case study that are in close proximity to its residing entity. For instance, take a look at this excerpt from the Lloyd s Hospital case study: We have 300 employees, most of whom work with a permanent contract, but some work on an hour-to-hour basis. Think of attributes as properties of entities. Therefore, from the excerpt above, you probably should have guessed Contract as being a good candidate. because it is a property of an employee. Some common issues in database design are: Should this be an entity or an attribute? Should this be an entity or a relationship? One might model the Contract as an entity, and later make the relationship Employees work under a Contract. This is not the model used in this chapter, but it is worth mentioning that there are many different ways to model the same information. Each variation of a model may work and be correct. This is part of what makes data modeling a painstaking process that requires patience. Whatever model is chosen, try not to jump ahead to the next stage of model- TIPEXAM Attributes on the Exam On the ing until you have considered some alternatives. exam you will not have to dream up Try to find out the attributes that fit each of the Patient, Employee, your own attributes, but you may have to select from a list of poten- Medicine, Machinery, Course, and Trainee entities. Test your results tial attributes and place them into with the results provided in Figure 2.2. If you missed an attribute or the correct entity. added an extra attribute that isn t found below, don t feel that it is wrong. Attribute decision is a hard choice and is varied from person to person, depending on your perspective on the scenario. Also
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