Data Modeling Essentials 2005 phần 6 pdf

... same as those we use for selecting good 2 76 ■ Chapter 10 Conceptual Data Modeling Simsion-Witt_10 10/11/04 8:49 PM Page 2 76 Chapter 10 Conceptual Data Modeling “Our job is to give the client not ... Unfortunately, much that is written and taught about data modeling makes this very naive assumption. Experienced data modelers do not try to solicit a data model directly, but...

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... format. 4 ■ Chapter 1 What Is Data Modeling? Figure 1.1 An information system. Report Program DATABASE Program data Report Program data data ProgramProgram data data 1 Data models can be presented ... 9 1.5.3 Data Quality 10 1.5.4 Summary 10 1 .6 What Makes a Good Data Model? 10 1 .6. 1 Completeness 10 1 .6. 2 NonRedundancy 11 1 .6. 3 Enforcement of Business Rules 11 1 .6. 4...

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... department data. Employee Number Qualification Description Qualification Year 01 267 Bachelor of Arts 1970 01 267 Master of Arts 1973 01 267 Doctor of Philosophy 19 76 70 964 Bachelor of Arts 1 969 2 261 7 ... HO Employee Number Qualification Description Qualification Year 01 267 Bachelor of Arts 1970 01 267 Master of Arts 1973 01 267 Doctor of Philosophy 19 76 70 964 Bachelor of Arts 1...

Ngày tải lên: 08/08/2014, 18:22

... structured approach to presenting data models. 6 4.12 Benefits of Using Subtypes and Supertypes ■ 129 6 First described in Simsion, G.C., “A Structured Approach to Data Modelling,” Australian Computer ... but whether the database structure, as specified by the data model, is the best place for them. Recall that one of the reasons we give so much attention to designing a sound data...

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... answer. 6. 2.2 Uniqueness Uniqueness is the most commonly cited requirement of primary keys. To reit- erate: you cannot build a relational database without unique primary keys. 1 86 ■ Chapter 6 Primary ... 10/8/04 7: 56 PM Page 152 5.4.4 Column Datatype and Length Requirements We now look at the translation of attribute types into column datatypes. If your DBMS does not support UDTs (use...

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... Bulwer-Lytton 8.1 Data Modeling in the Real World In the preceding chapters, we have focused largely on learning the lan- guage of data modeling without giving much attention to the practicalities of modeling ... minimum list. 8.2.1 Recognition of Data Modeling Let us repeat what we said in Chapter 1: No database was ever built with- out a data model. Unfortunately, many datab...

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... accepting a data model. 10. 16 Testing the Model with Sample Data If sample data is available, there are few better ways of communicating and verifying a data model than to work through where each data ... time they can devote to using the data model properly! 11 .6. 2 One-to-One Relationship Implementation A one-to-one relationship can be supported in a relational database by im...

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... include historical data in the same table as the corresponding current data, it is likely that different queries access current and historical data. Placing current and historical data in different ... improve the performance of queries on current data. You may prefer to include a copy of the current data in the historical data table to enable queries on all data to be written w...

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... of History, 1 968 15.1 The Problem Few areas of data modeling are the subject of as much confusion as the handling of time-related and time-dependent data. Perhaps we are modeling data for an insurance ... expect that the data to support this process rule is going to be held in the database. 14.2.3 What Rules Are Relevant to the Data Modeler? The data modeler should be concer...

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... dimensions. (Figure 16. 2 in Section 16. 6.2 shows an example.) The data modeler is required to fit the data into this 16. 2 Characteristics of Data Warehouses and Data Marts ■ 479 Simsion-Witt_ 16 10/8/04 ... 10/8/04 8:08 PM Page 502 This page intentionally left blank 16. 6 Modeling for the Data Mart 16. 6.1 The Basic Challenge In organizing data in a data mart, the basic...

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