Table 23-5 is a glossary of terms that you can review and refer to as necessary. There are a few terms in here that appear later in the chapter.
Table 23-5. Relational database glossary
Name |
Description |
---|---|
attribute |
A column in a table, e.g., the “Name” attribute. |
cardinality |
The number of rows in a relation. |
database integrity |
You maintain database integrity by grouping statements in a “transaction” that is either executed as a whole, or has no part of it executed. |
degree |
The number of columns in a table. |
domain |
The set of permissible values for an attribute. |
entity integrity |
The requirement that key attributes never contain a null. |
first normal form |
A table in which no attributes have lists of data items. |
foreign key |
The attribute or group of attributes in one table that form a primary key for some other table. |
join |
An operation that combines the data in two or more tables by using foreign keys in the first table to access related data in a subsequent table. This is an “inner join” or “equijoin”. |
prepared statement |
An SQL statement which is cached in native code form to allow faster processing. |
primary key |
The attribute or group of attributes that together uniquely identify a record in a table. |
referential integrity |
The requirement that all foreign keys are present in the table where they are a primary key. |
relation |
A table in a relational database. It corresponds to a file of records. |
relational database |
A collection of relations in third normal form. |
second normal form |
A table is in second normal from when it is in first normal form and also every non-key attribute depends on the primary key. |
stored procedure |
A group of related SQL statements, which are kept in precompiled form inside the database, and can be invoked just like a method call. |
third normal form |
A table is in third normal form when it is in second normal form and also all non-key attributes are independent of each other. |
trigger |
A trigger is an SQL statement that is stored in the database, and that executes automatically when a specified event occurs in the database, such as a column update. It will usually be some kind of automatic delete, insert, or update of some other attribute. |
tuple |
A tuple is a row of related data in a table. It is essentially a record of related data. |
Once we have our tables, SQL is the language we use to access and process them. The JDBC library is a way of connecting to a database, shipping it SQL statements, and getting back the results in a form that Java can process. We will shortly present a primer on SQL, showing the highlights of the language for those who have never seen it before. First we need to download the open source Mckoi database, which includes a GUI tool for submitting SQL queries.
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