ASSIGNMENT 2

Assignment 2

(a) Open the Northwind database within Microsoft Access. Write a brief discussion of ways in which the business may change rendering this database temporarily obsolete.

Figure 1: Northwind Database

How to Open Northwind Database

The Northwind database contains some great sample tables, queries, reports and other database features. Here's how to install it.

Start Microsoft Access

When the opening screen appears, make sure that Open an Existing File is selected.

Choose Northwind Sample Database from the menu.

If Northwind was previously installed it will open immediately. Otherwise, click Yes to install it. You may be prompted to insert your installation CD.

Ways in Which the Business May Change Rendering this Database Temporarily Obsolete

There are numerous situations in which the Northwind database cannot provide a precise and unambiguous answer to some of the queries that business may wish to pose. The potential sources for the difficulty vary. These include examples such as measurement and recording errors, missing data, incompatible scaling, obsolescence, and data aggregation of one kind or another. Northwind database may use different approaches to this problem. These range from a consistent way of handling a place-holder “value not known” to Lipski's recent work (Lipski, JR., W., 1979) on dealing with the truth value “possible” in an extended propositional calculus.

In database management systems (particularly relational ones) with facility for supporting views, such facility can be used to support statistical processing. Basically, the idea is to treat the prior information on the distributions as an additional database. A query on the idealized world is then transformed by view mapping into a query that spans both the real database {h(e), e E E } and the statistical database that contains the prior information. It is important to note the difference between such a procedure and the query transformation procedure suggested by the separation principle. The query transformation involved in view mapping is much simpler, but the resulting query is more complex. In effect, one is using the view-support and query-processing facilities that normally exist to achieve the computation needed to transform an ideal-world query into a real world query.

For example, the existence of replicated data, especially in distributed systems, suggests the use of redundance to reduce uncertainty. However, the cost of using more than one copy is large and must be kept to a minimum by strategies provided by sequential analysis. Another issue concerns how the a priori distribution information is to be acquired. In some cases it must be done empirically by sampling. However, in many interesting cases (e.g., obsolescence) the distributions can be obtained by modeling the process by which the data ambiguity is introduced. However, we believe that the purely theoretical speculation should await some attempts at implementation for a major application where problems of incomplete information actually arise.

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