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Glossary
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Cloudscape Glossary
- ACID
- The four properties of transaction control: Atomicity,
Consistency, Isolation, and Durability.
- Agreement
- A situation in which the only difference between the
corresponding data in two databases is latency. See Latency.
- Applet
- A Java program that is executed by a browser, as opposed to a
stand-alone Java application.
- Atomicity
- The A in ACID. The property of transaction control that means
that either all or none of the statements in a transaction are
executed.
- Auto-commit mode
- A state within a JDBC application that means each individual
SQL statement is treated as a transaction and is automatically
committed when executed. To group two or more statements
into a transaction, you must turn off auto-commit mode in the
application, then explicitly commit a transaction. In a
Cloudscape application, auto-commit causes cursors to close.
- Backing index
- An index that Cloudscape creates to enforce a primary key,
unique, or foreign key constraint. So called because the index
helps "back up" the constraint. Indexes created in this way are
no different from indexes that you create with explicit
CREATE INDEX commands, except that they have system-
generated names.
- Blob
- In RDBMS systems, a binary large object. Cloudscape does
not support the SQL data type BLOB, but does support
some of the JDBC Blob methods that provide a logical
pointer to the large object rather than to the object itself.
- Bulk import
- Populating a table by importing data from a flat file instead of
through insert statements.
- Bulk export
- Exporting the contents of an entire table or any subset of data in
a database to a flat file using a Cloudscape-provided utility.
- Check constraint
- A boolean test applied to each row of a table on an insert or
update to validate it.
- Client/server environment
- When multiple applications connect to Cloudscape over the
network, they are said to run in a client/server environment.
Cloudscape runs embedded in a server framework that allows
multiple network connections. (The server framework itself
starts up an instance of Cloudscape and, strictly speaking, it is
running in an embedded environment; the client applications,
however, are not.)
- Class path
- A list of directories or zip files to search for class files.
- Clob
- In RDBMS systems, a character large object. Cloudscape does
not support the SQL data type CLOB, but does support
some of the JDBC Clob methods that provide a logical
pointer to the large object rather than to the object itself.
- Commit
- An operation that completes a transaction and causes all
updates made during the transaction to be permanently written
into a database.
- Concurrency
- Multiple users or programs simultaneously sharing the same
database. Transactions and data locks are used to give each of
these a consistent view of the database.
- Conflict
- In Cloudscape synchronization, a change submitted by a target
database that, if allowed to apply at the source, would corrupt
the data.
- Conglomerate
- A unit of storage within a Cloudscape database, either a table or
an index.
- Connection
- A session with a database opened by a JDBC application
program. Only one transaction at a time can be associated with
a connection.
- Consistency
- The C in ACID. Consistency means that each transaction starts
in a consistent state and ends in a consistent state. One
transaction cannot "see" the changes caused by another
transaction until that other transaction completes.
- Constraint
- In a database, a rule that ensures the integrity of data.
Constraints can apply to columns or tables. An example of a
-column-level constraint is that the values it contains must be
unique.
- Cursor
- A construct used to reference the current position in a result.
SQL defines a cursor mechanism that can be used through
JDBC to do positioned updates and deletes.
- Database
- A Cloudscape database stores data as SQL-92 data types and
Java objects. A Cloudscape database contains dictionary
objects that organize the data. Cloudscape databases are stored
in files in folders named after the database.
- Database-side method
- A Java method invoked in SQL-J and executed by Cloudscape.
- Database-side JDBC method
- A Database-side method that executes SQL-J statements,
usually using a nested connection.
- Database class loading
- When you store application logic (in the form of jar files) in a
database, you can configure Cloudscape (and your application)
to load classes from the database instead of from the user's
class path.
- Database connection URL
- In JDBC, a URL that you specify as an argument to the
-DriverManager.getConnection method call and that returns a
connection to a database. Cloudscape's database connection
URL allows you to specify attributes to the connection.
- DBMS
- Database management system. Software that manages
databases. Cloudscape is a DBMS, and it can run as an
embedded database system under the same JVM as the database
application program, or it can run as a database server, under a
different JVM, or even on a different machine from that of the
application.
- DDL
- Data Definition Language. A subset of SQL commands that
create dictionary objects.
- Dependency
- The relationships among prepared statements and dictionary
objects in a database. Cloudscape tracks the dependency that
publications, stored prepared statements, and prepared
statements have on the dictionary objects they access. If
dropping or modifying a dictionary object would cause an open
prepared statement to be invalidated, the change is not
permitted.
- Dictionary object
- A user-defined entity contained in a Cloudscape database.
When creating a database, users create and name dictionary
objects such as tables, indexes, constraints, views, and stored
prepared statements. Information about these dictionary objects
is stored in the Cloudscape system tables, sometimes called the
data dictionary.
- Disk encryption
- Encrypting a Cloudscape database, which is otherwise stored as
clear text. You must specify a boot password when you boot the
database in order to connect to it.
- Durability
- The D in ACID. Durability means that a transaction's
committed updates must be durable, even in the case of
hardware or software failure.
- Durable transaction
- In Cloudscape synchronization, a transaction that has
committed at the source.
- Dynamic parameter
- A parameter to a PreparedStatement whose value is unspecified
when the statement is prepared. A dynamic parameter is
represented by a question mark (?) in the SQL-J language.
- Embedded environment
- When an application starts up an instance of Cloudscape within
its JVM, the application is said to run in an embedded
environment. In this environment, only a single application can
connect to a database at one time, and no network access
occurs. The end-user may not even be aware of the database.
- Environment
- The way your application interacts with Cloudscape.
Sometimes referred to as a framework. The two environments
are Embedded environment and Client/server environment.
- Exclusive lock
- When a statement modifies data, its transaction holds an
exclusive lock on data that prevents other transactions from
accessing the data.
- External virtual table
- A virtual table in a FROM clause of an SQL-J statement in
which a constructor of a class that fulfills Cloudscape's Virtual
Table Interface (VTI) requirements makes external data
available to a SELECT statement.
- Field access
- In Cloudscape, accessing the static field of a Java class, or
accessing the static or non-static field of an instance of a class.
The class does not need to be serializable or stored in the
database.
- Hash join
- A join operation in which Cloudscape uses a hash table for
performance reasons. It is suitable for joins in which the outer
table's values are joined with single rows in the inner table, and
values in the inner table are unique. See Nested loop join for
comparison.
- Index
- A dictionary object that helps the DBMS find rows of a table
quickly based on the values of one or more columns.
- Inner table
- In a join operation, a table that is not the outermost table. See
Outer table for more information.
- Isolation
- The I in ACID. Isolation means that the database must give each
connection data that appear to be unaffected by other
transactions until the transaction commits.
- Java data type
- A Java class used within a Cloudscape system for storing
instances in a table or for method invocation, or both. Also
known as a user-defined data type. The class must be available
to the Cloudscape system.
- Java stored procedure
- You may hear from other vendors about stored procedures
written in Java that are declared with a statement such as
CREATE PROCEDURE. These stored procedures are called
Java stored procedures. In Cloudscape, you can call any Java
method without having to declare it. In this documentation, we
call such methods database-side methods, because you have the
DBMS execute them. Such methods do not have to be stored in
the database.
- JDBC
- The java.sql package, which is a set of classes and interfaces
that make it possible to access databases from a Java
application. (JDBC is not an acronym.)
- JDBC driver
- A Java class that implements the JDBC driver interface and is
loaded into the JDBC driver manager. The core Cloudscape
product comes with a built-in, local JDBC driver.
- JDBC method
- A method in a Java class that uses JDBC calls to access data in
a Cloudscape database. When invoked from within
Cloudscape, the method is called a database-side JDBC
method.
- JDK
- Java Development Kit. The software released by JavaSoft to
support the Java environments. The JDK includes the Java
compiler and interpreter and many Java libraries.
- JIT
- Just-in-Time compiler. An alternative to a JVM; instead of
interpreting byte code, it compiles it into machine code on the
fly.
- Join
- The basic relational operator that allows data from more than
one table to be combined.
- JRE
- Java Runtime Environment. Consists of the Java virtual
machine, the Java platform core classes, and supporting files. It
is the runtime part of the Java Development Kit--no compiler,
no debugger, no tools. The JRE is the smallest set of
executables and files that constitute the standard Java platform.
A JRE is a JVM targeted primarily for developers who will be
bundling the JRE with their applications for deployment.
- JVM (Java Virtual Machine)
- The program that interprets the byte codes of a Java application.
A JVM is part of a JDK.
- Keyword
- A word that is part of a DBMS's command vocabulary. The
SQL-92 standard has defined a large number of keywords.
Some are reserved, which means that they cannot be used for
another purpose within an SQL statement unless delimited, and
some aren't. Cloudscape has its own additional keywords.
- Latency
- In a synchronized system, the time between a change at one
database and the corresponding change at another database.
- LDAP
- Lightweight Directory Access Protocol. It provides an open
directory access protocol running over TCP/IP. You can
configure Cloudscape to authenticate users through an LDAP
Directory Server.
- Leaf level
- The bottom level of a BTREE index.
- Locale
- Locale in the Java platform refers to an instance of a class that
identifies a particular combination of language and region. If a
Java class varies its behavior according to Locale, it is said to be
locale-sensitive. In Cloudscape, you can assign a locale to a
database.
- Lock
- When a transaction views or modifies data, Cloudscape locks
rows or tables to enforce the Isolation of this transaction from
other transactions. Cloudscape uses the following kinds of
locks: Exclusive lock, Shared lock, and Update lock.
- Long row
- A row that spans more than one database page. Cloudscape
automatically overflows long rows that do not fit on a single
database page.
- LUCID
- Logic up, consistent information down. This acronym describes
Cloudscape's synchronization model.
- Metadata
- Information about a database or a DBMS. Examples: the kind
of functionality a DBMS provides, the types of data in the
database, or information about a result set. In JDBC, you call
the methods of the DatabaseMetaData or the
ResultSetMetaData class to get this information.
- Method
- A procedure associated with a class or interface that defines one
of the legal operations on instances of the class or interface. In
Cloudscape, you can invoke methods that belong to a class
stored in the database or to any class visible to Cloudscape.
- Method Invocation
- In Cloudscape, invoking a Java class method. The method can
be either static or not static.
- Nested connection
- The "current" connection "re-used" by a database-side JDBC
method. Such methods re-use the current connection so that
statements that they execute are contained by a single
transaction.
- Nested loop join
- The typical way that Cloudscape executes joins. Cloudscape
loops through the inner table using the best access method
available (usually an index) for every qualifying row in the
outer table.
- Null
- A data value that is unknown or unspecified. Java has a
distinguished null object value, and SQL has a distinguished
null value that represents the absence of an actual value.
- Object
- An instance of a Java class. An object can be stored in a
Cloudscape database if it implements the java.io.Serializable
interface.
- Optimization
- A process in which the DBMS makes the best (optimal) choice
of access paths and join order. True query optimization means
that the DBMS will usually make the best choice independent
of how the query is written. Cloudscape's optimizer usually
makes a good decision; you may sometimes want to override it.
- Orderable Java data type
- In Cloudscape, Java data types that can be used in ordering
operations such as ORDER BY, GROUP BY, DISTINCT,
UNION and > and < comparisons. You can also create indexes
on orderable Java data types.
- Outer table
- In a join operation, the table that Cloudscape looks at first. It is
best if the outer table is the one for which the fewest rows
qualify, since Cloudscape will look up values in an inner table
or tables for every qualifying row in the outer table.
- Package
- In a Java library of classes, a group of classes and interfaces.
Package names are separated by dots and stored in directories
that match these names. When specifying Java classes within an
SQL-J statement, you must specify the package name along
with the class name.
- Page
- A user-configurable unit of storage within a conglomerate.
Conglomerates are made up of multiple pages.
- Positioned update/delete
- A mechanism to update or delete the row at the current position
through an SQL cursor.
- Prepared statement
- An SQL statement that has been compiled for efficiency. The
SQL processor parses and analyzes the statement and produces
an execution plan for the prepared statement.
- Primary key
- The columns in a table that uniquely identify the rows in the
table.
- Property
- In the Java world, a configuration parameter. You can set
properties for Cloudscape systems, databases, queries, or single
conglomerates.
- Provisional transaction
- In Cloudscape synchronization, a transaction that has
committed at a target but has not yet committed at the source.
- Publication
- In Cloudscape synchronization, a dictionary object in a source
database that defines a set of target databases. Source databases
have publications; target databases subscribe to publications.
- Pure Java
- Refers to a program written entirely in Java. The tag "100%
Pure" carries additional restrictions.
- Query
- The basic part of a SELECT statement.
- RDBMS
- Relational database management system. A DBMS that
supports the SQL standard is considered relational.
- Refresh
- In a Cloudscape synchronization, a request issued by a target
database to submit changes to the source and copy source
changes to the target. All synchronization in Cloudscape is
done using the refresh operation.
- Result set
- The rows that satisfy the conditions of a query. Cloudscape
returns these rows through the JDBC interface in a JDBC
ResultSet object. You can access the result set one row at a
time.
- Rollback
- Undoing the changes made by a transaction before it commits.
You can initiate a rollback by explicitly calling the JDBC
Connection method rollback.
- Row-Level locking
- A locking system in which Cloudscape locks only rows, not
entire tables. Row-level locking allows greater concurrency.
Cloudscape uses locking to present data in a consistent state to
multiple users or applications.
- Schema
- (1) A description of the dictionary objects in a database and
their attributes.
-
- (2) A database entity that consists of one or more tables, views,
triggers, and so on. A schema provides a way to group a subset
of tables within a database. A schema name qualifies a table
name within a database.
- Serialization
- A Java mechanism for writing objects to an output stream.
Cloudscape uses the serialization mechanism to store objects in
a database.
- Server
- A machine that provides services of some kind to client
machines on the network. A database server is a DBMS that
provides services to applications that reside on client machines
on the network. Cloudscape can be deployed as a database
server by using Cloudconnector or another server framework.
- Server framework
- An application that enables multiple connections to
Cloudscape. Unless Cloudscape runs inside a server
framework, only one application at a time can access a
Cloudscape database. Cloudconnector and RmiJdbc are server
frameworks.
- Shared lock
- When a statement reads data without making any
modifications, its transaction obtains a shared lock on the data.
Another transaction that tries to read the same data is permitted
to read, but a transaction that tries to update the data will be
prevented from doing so.
- Source
- In a Cloudscape synchronization system, the database from
which data are copied to other databases (called targets).
- SQL
- A standardized database language for specifying queries and
updates to databases. (At one time, SQL stood for Structured
Query Language; now it's another one of those acronyms, like
JDBC, that do not stand for anything.)
- SQL-J
- Cloudscape's Java-extended dialect of SQL-92.
- SQL-92
- The version of SQL standardized by ANSI and ISO in 1992.
- SQL-92 entry-level
- A subset of full SQL-92 specified by ANSI/ISO that is
supported by nearly all major DBMSs today. JDBC compliance
requires entry-level SQL compliance and defines escape syntax
and metadata routines for more advanced features.
- SQLExceptions
- Errors generated during database access.
- SQLState
- Standard error code, defined by SQL-92, associated with
SQLExceptions.
- SSL
- Secure Socket Layer. A protocol standard in wide use today for
negotiating a secure connection.
- Static method
- A method that is associated with a class rather than an instance
of the class.
- Stored procedure
- In some DBMSs, procedural code, written in SQL, executed by
the DBMS. In Cloudscape, you execute Java methods instead
of stored procedures.
- Stored prepared statement
- SQL-J statements named by the user and stored in a
precompiled state for performance reasons.
- Streaming column
- Data stored via an input stream or retrieved via an output
stream.
- Synchronization
- An operation that keeps distributed databases in agreement.
- System
- Semi-persistent environment for a Cloudscape session. Also a
location; the default location for Cloudscape databases and
configuration properties.
- Target
- In a Cloudscape synchronization system, a database created
from a publication. See Publication.
- Tear-Off Database
- A target database.
- Transaction
- A sequence of JDBC/SQL calls within a single connection that
constitute an atomic unit of work, that provide atomicity,
consistency, integrity of data, and durability of database
changes. In Cloudscape, transactions are handled entirely by
JDBC calls.
- Update lock
- When a user-defined update cursor reads data, its transaction
obtains an update lock on the data. If the cursor updates the
data, the update lock is converted to an exclusive lock. If the
cursor does not update the row, the row is either release or the
lock on the row is downgraded to a shared lock until the
transaction is committed.
- URL
- Uniform resource locator. First used on the WWW to identify
HTML documents. A specialized form of URL is used by
JDBC to identify databases. See Database connection URL.
- User-defined data type
- See Java data type.
- Virtual Table Interface (VTI)
- A Cloudscape construct that provides an interface to external
data within an SQL-J statement. Classes that fulfill the VTI
requirements can be used in the FROM clause to provide data to
a SELECT statement. Cloudscape's bulk import utility,
COM.cloudscape.vti.FileImport, is an example of such a class.
- WHERE clause
- The portion of an SQL statement that allows the statement to
retrieve a subset of rows that meet a particular set of conditions.
Retrieving a subset of rows is sometimes called restriction. The
WHERE clause requires a search condition (one or more
predicates combined with AND, OR, and NOT) to specify the
conditions under which you want rows to be chosen for
inclusion in your set of data.
In a Cloudscape synchronization system, a table in a
publication can include a WHERE clause.
- Work unit
- Two static Java methods, one at the target and one at the source,
that perform a single logical operation and are referred to by a
single alias.
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