Lecture
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numbers with fixed and floating point. Individual implementations are sometimes able to work with other data types as well; however, the representation of information in the form of graphical elements or strings of arbitrary length is not directly supported.
Analysis of Data Schemes
Date poses the following question: "Suppose we are given a set of data that must be arranged in a database. How do we determine a suitable logical structure for this data? In other words, how do we determine the relations and attributes? This is precisely the problem of database design" [19]. It turns out that identifying the key abstractions of a database in many ways resembles the process of identifying classes and objects. For this reason we will begin the development of the inventory tracking system directly with object-oriented analysis, in the course of which the structure of the database will take shape, rather than first setting about creating the database schema and then deriving the object model from it.
Let us begin with the list of principal abstractions we have already enumerated. Applying Rumbaugh's rules to it, we obtain the following database tables (first let us list those of them that correspond to the roles of the groups taking part in the operation of the system):
Next come the tables reflecting the classification of products and their availability in the warehouse:
And, finally, we introduce tables for the document flow:
We did not create tables for the classes Report and Transaction - the results of the analysis suggest that objects of these classes do not need to be stored.
At the next stage of analysis the composition of the attributes of all the tables listed can be determined in detail. There is probably no sense in discussing these questions in the pages of this book; we have already dwelt on the most interesting properties of these abstractions (see Figure 10-4), and the remaining attributes offer little that is new from the standpoint of the system's architecture.
Часть 1 10 Client-Server Architecture: Inventory Tracking 10.1. Analysis
Часть 2 - 10 Client-Server Architecture: Inventory Tracking 10.1. Analysis
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