April 2003
Beginner to intermediate
380 pages
12h 25m
English
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Relational Modeling Constructs
Before we discuss the mapping between Java classes and a relational schema, we will first provide a brief summary of the modeling constructs found in relational schemas. This is not meant to cover all aspects of a relational schema; it will simply define the terms we use in this chapter.
A relational schema is organized as a set of tables. A table is usually defined for each entity in the application domain you are modeling. When you design an object model, an entity is represented by a class. Each table consists of rows and columns. A row contains the data for a specific instance of an entity being modeled. A column contains the values for one of the attributes of the entity. A table cell is the intersection of a particular row and column in the table, and it contains the value of an attribute for a specific entity instance.
The type of a column is the same for all rows of a table. Relational databases do not support Java’s capability for a field to reference one of many different types. ANSI SQL 92 defines a standard set of supported column datatypes. Relational database products support these standard datatypes and usually support their own additional, proprietary datatypes. One issue developers often contend with is the use of a datatype that is specific to one database product but not supported by another. JDO helps insulate your applications from these datatype differences, since you only deal with Java types, which are then mapped to the various ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.