Components required for time variant data according

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Oracle 12c: SQL
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Chapter 6 / Exercise 7
Oracle 12c: SQL
Casteel
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Components Required for Time-Variant DataAccording to the textbook, data changes are managed by replacing the existing attribute value with the new value, without regard to the previous value. However, in some situations, the history of values for a given attribute must be preserved. From a data modeling point of view, time-variant data refer to data whose values change over time and for which you must keep a history of the data changes (Coronel, Morris, & Rob, 2013). In this scenario, were PGSH wants to keep track of fields for both policy enforcement and training managements, close monitoring needs to be put in these variant fields like certifications, skills, jobs history, salary history and anything related to the fields they want to keep track of. Keeping time variant data will change the model a bit, to adjust the need for it. In the new model, a new entity will be created on a one to many (1: M) relationship with its original entity, where the original one holds the new or updated value and the effective date of it while the new entity will hold any "old values." In this example, the most important or relevant to what PGSH wants to do is for training history and certifications history. But other will need to be considered as well, as history data for job and
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Oracle 12c: SQL
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Chapter 6 / Exercise 7
Oracle 12c: SQL
Casteel
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DATABASE MODELING AND NORMALIZATION5salary. Figure 1 represents the diagram of a one to many (1: M) solution to hold salary, job, and training history data for each employeeFigure 1. One to Many (1: M) Solution keeping time-variant data for each employee.Normalization Process to ensure 3NF level of NormalizationThere are three (3) levels of normalization in a database and each and one of them guarantees and set fundamental rules to ensure that data will not be redundant, corrupt, incomplete, and reliable. Each level builds on the last, and while going to these steps, 1NF, 2NF and 3NF respectively we ensure all that normalization entails. The first normal form (1NF) states that: Every column in the table must be uniqueSeparate tables must be created for each set of related dataEach table must be identified with a unique column or concatenated columns called the primary keyNo rows may be duplicated
DATABASE MODELING AND NORMALIZATION6No columns may be duplicatedNo row/column intersections contain a null valueNo row/column intersections contain multivalued fieldsOn the other hand, the second normal form (2NF) has two basic requirements:There is no redundancy of dataData dependencies are logicalFinally, the third normal form (3NF) states that all column reference in referenced data

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