Oracle Essentials [Electronic resources] : Oracle Database 10g, 3rd Edition نسخه متنی

14.2 The Oracle Database and the Internet

There are several areas of functionality
in the Oracle database that relate, either directly or more
peripherally, to using the database in connection with the Internet.
For example, you can:

Access an Oracle database through a web server, which is included
with the product

Use Internet-era standards, such as the Java programming environment
or XML-formatted information

Use a new development tool in Oracle Database
10g to build browser-based applications

14.2.1 Oracle HTTP Server

Oracle HTTP Server (OHS) is a web server
that is included with the Oracle database. The Oracle HTTP Server is
essentially the same HTTP server that is included as part of Oracle
Application Server. Based on the Apache web server, it has different
mods that support different types of
functionality.

The version of Apache used in OHS is 1.3.x, where x is the latest released Apache version. For Oracle Database 10g, the version is 1.3.28.

Before Oracle Database 10g, OHS came as an
integrated part of the database. Oracle Database 10g
includes a standalone version of OHS, which has only some modules
(mods)for example,
mod_plsql, mod_cgi,
mod_perl, and others. (Previous versions of
Oracle came with a version of OHS that included a larger number of
mods.) The standalone version comes on a
separate CD-ROM and is installed separately.

The mod most directly related to the Oracle
database is
mod_plsql,
which provides a connection to the PL/SQL engine within the Oracle
database. This module allows a user to call an Oracle PL/SQL
procedure in the database.

When a user calls an Oracle procedure, OHS uses
two types of configuration information:

A Data Access Descriptor (DAD), which
defines the Oracle database and username/password combination used to
access the database

Some form of pass-through identifier, which routes the call to a
PL/SQL procedure

The connection to the database is established through the DAD, which
identifies the target database and either uses a specific username
and password combination or prompts the user for a username and
password. Each PL/SQL agent is associated with a DAD, and each DAD
can be associated with several agents.

OHS is configured to listen on a particular port. Requests come in
the form of URLs consisting of the name of the server, the port
number of the server, the name of the PL/SQL agent that will service
the request, and the name of the stored procedure that is to be
executed. For instance, suppose that the server name is
homeserver, the PL/SQL agent that is to service
the request is netu, and the listener is listening
on port 4000. A request for a stored procedure called
return_time would look like the following:

http://homeserver:4000/netu/return_time

If this stored procedure accepts parameters, those parameters can be
included in the standard URL syntax following the name of the
procedure. Of course, this stored procedure would be designed to
return HTML code in response to this call.

14.2.2 Standards Support

The Internet era has
popularized a new set of standards. The Oracle database provides
functionality to support most of these standards, such as the HTTP
server mentioned in the previous section. Two standards have a
significant amount of supportJava and XML.

14.2.2.1 Java in the database

The Oracle database includes its own
Java Virtual Machine, called the Oracle JVM (formerly known as
JServer). Java
programs can be developed with any standard Java tool. You can load
either the Java source code or the
"compiled" version of the Java
program in its .class format into the database.

The Oracle JVM runs in the same process space as the standard
Oracle database and can directly access the
information in the database buffers, which can help to improve the
performance of data access through Java. It runs as part of a
database session, so there is no need to establish an explicit
connection to the Oracle server. Because it's part
of the Oracle server, the Oracle JVM uses the
same security and authentication methods as its host database.

The Oracle JVM Accelerator included with
Oracle is a native code compiler that can
deliver performance for Java binaries that's close
to the performance of compiled C code. It operates by converting Java
binaries into specialized C programs, which are then compiled into
native libraries. Oracle claims that the garbage collection process
(an integral part of a Java Virtual Machine) implemented in the
Oracle JVM also provides better performance than most other Java
virtual machines.

Enterprise JavaBeans, or EJBs, are a
type of Java program that can be run on a server machine within the
context of an EJB transaction server. The EJB
transaction server provides system-wide services for all EJBs, such
as transaction and state management and communication with other EJB
servers. The EJB server implemented by Oracle
can use some of the internal management capabilities of
the Oracle database server, such as those in the shared server.
Oracle includes automated tools to load and
publish EJBs, which makes them easier to use with Oracle.

14.2.2.1.1 PL/SQL and Java

PL/SQL
procedures can be called from any Oracle JVM application through the
SQLJ interface embedded in the server (the next section describes
SQLJ). However, you have to
"publish" the top-level Java
methods;
publishing
creates, in effect, a PL/SQL interface for the methods and thus makes
them available to PL/SQL procedures. Once the wrapper is created, you
can use the Java application just as you would any other PL/SQL
procedureeven as part of a standard SQL statement.

With Oracle Database 10g, you can call Java
procedures in the database directly, without the need for a PL/SQL
wrapper.

By now, there have been two major releases since Java was introduced in the Oracle database, so it is probably safe to assume that both PL/SQL and Java will continue to exist as procedural languages that can be run inside the Oracle database.

The JPublisher tool, which comes as a part of
Oracle8i and beyond, is used to create the
interface between user-defined datatypes and Java wrapper classes.
This capability allows you to extend the object-relational datatypes
you may have already created with Oracle to the Java environment, or
to create user-defined datatypes that can act as persistent storage
for the Java objects you use in your Java applications.

14.2.2.1.2 JDBC and SQLJ: Java's 3GL interfaces

Oracle includes two application programming
interfaces to data from the Java environment:
JDBC
and SQLJ. JDBC is a fairly low-level interface that gives Java
developers complete control over the interaction between Java
applications and data in the Oracle database.
JDBC is the functional equivalent of existing APIs such as ODBC. Like
ODBC, JDBC is a vendor-independent API.

The JDBC interface is standard, but Oracle offers it in three flavors:

A thin client, 100% Java version

This version is compact (150 KB compressed) and ideal for clients
that use only Java.

A slightly fatter client version that is based on the Oracle Call Interface (OCI)

This version requires some form of Oracle networking software that
supports OCI.

The in-database JDBC driver (JDBC KPRB)

Java code uses the JDBC KPRB (Kernel Program Bundled)
version to access SQL on the same server.

The OCI version of the JDBC interface is a little faster than the
pure Java version, so it is most appropriate for use in places like a
middle-tier component. The server-side JDBC driver is used for Java
stored procedures that run inside the Oracle
server.

Oracle also includes the
SQLJ interface. SQLJ is
a Java library that lets developers use embedded SQL statements in
their Java applications. The SQLJ interface works like the Pro*
interfaces that already exist for other 3GL languages, such as Pro*C
and Pro*COBOL, but unlike these interfaces, SQLJ is an industry
standard. You can simply insert SQL statements into your Java code,
and the SQLJ translator will translate those calls into their
underlying JDBC equivalents.

There are a couple of significant differences between JDBC and SQLJ.
Because JDBC simply submits SQL statements as strings, any problems
with your SQL syntax won't be found until they are
detected by the Oracle database at runtime. With SQLJ, the translator
parses the SQL statements and returns errors. On the other hand, SQLJ
can be used only for static SQL statements, while JDBC can submit
dynamically constructed SQL statements. Much of the flexibility built
with dynamic SQL statements can be implemented using bind variables,
but there may be times when you need to use the JDBC interface. You
can easily mix and match SQLJ and JDBC in your Java application, but
the presence of any SQLJ code will require the use of the translator.

14.2.2.2 XML

XML is a kind of evolutionary
standard. It is a text-based markup language, like HTML, but it can
be extended to describe a virtually unlimited number of datatypes and
structures. Because of this flexibility, it has become a popular
standard format for data storage and exchange.

The Oracle database supports a variety
of XML standards. It also provides the functionality of a complete
XML database, XML DB, as part of the Oracle database. See the later
section describing XML DB.

14.2.2.2.1 XML standards

Oracle includes a number of features that support XML, such as its
XDK (or XML development kit) for Java, C,
C++, and PL/SQL. The XDK lets developers send, receive, and interpret
XML data from applications written in their respective languages.
From Oracle9i on, the XDK also supports the XML
schema standard for defining the datatypes for a particular XML
document, which replaces the old method of using Document Type
Definitions (DTDs). Since Oracle9i, all versions
of the XDK also include two JavaBeans (or components), the DBAccess
Bean and the DBView Bean, that make it easier for developers to
define access to and view XML data stored in the database.

Oracle9i also
provided these XML-related features:

XML class generators for Java and C++

Create classes from XML schema definitions.

XML SQL utility

Supports
reading and writing XML data to and from the database using SQL. You
can also get most of this functionality by using the DBMS_XMLGEN
built-in package.

XSQL servlet

Generates XML
documents from one or more SQL queries and uses XSL stylesheets to
format the results. This servlet can also be used to insert, update,
and delete data using XML.

The Oracle9i release included the new XMLType
datatype, which we described in Chapter 4. This datatype allows
native storage of XML documents in the Oracle9i
and later database versions.

Oracle Database 10g continues the improvement in
XML support by adding the ability to use multibyte character sets
with XML for internationalization.

14.2.2.2.2 XML DB

XML DB is a term for a group of XML features that were introduced as
part of Release 2 of Oracle9i.
XML DB consists of
four key areas:

XMLType

Described in Chapter 4, the
XMLType
datatype indicates to the Oracle database that the contents are XML
data, so that specific XML operations, such as XPath-based searches
and updates, can be performed on it.

Support for XMLSchema

An XMLSchema is a
description of the specific contents and types in an XML document,
and can be used as a constraint for an XMLType column. Oracle can
also use the information contained in an XMLSchema to automatically
shred documents into a series of objects and store them in the
database with no loss of information. Oracle XML DB is then able to
use the information contained in the XMLSchema to optimize
XPath-based queries and updates over the content of XML documents
stored in the database.

XML DB repository

The XML DB
repository allows a URL to be used to locate an XML document, or to
define relationships between XML documents stored in the Oracle
database. The XML DB repository includes a hierarchical index that
allows a URL-based access to be as efficient as a primary-key based
access. The repository also includes support for HTTP, FTP, and
WebDAV protocols, which are used by many popular
applicationsfor example, Windows Explorer, Internet Explorer,
Microsoft Office, and XML editors such as Corel's
XMetaLto access content stored in the Oracle database without
requiring Oracle software on the client.

SQL/XML

SQL/XML provides a
standardized method for generating XML documents directly from a SQL
statement.

14.2.3 Simplified HTML Applications Development

Oracle offers a wide set of development tools, which we described in
Chapter 1. Oracle Database
10g includes a new development tool specifically
designed to create and run applications in a browser environment,
HTML DB.

HTML DB harks back to the days of WebDB, which provided a way to
develop HTML-based applications. Like WebDB, HTML DB gives you a
series of browser-based wizards that help you create standard
application components.

HTML DB uses the concept of a
workflow
as the organizing principle for sets of these components. The
workflow provides a menu interface, typically using tabs, as shown in
Figure 14-1.

Figure 14-1. An HTML DB application

Within a workflow, you create various pages, which implement specific
pieces of functionality, such as reports or data entry or a tree
structure used for hierarchical browsing. You can link different
pages together within a workflow.

HTML DB lets you provide security for pages and workflows to limit
access to HTML DB pages. Workflows and pages have templates that
control their look and feel.

Two other aspects of HTML DB provide functionality of interest to
DBAs as well as developers:

SQL Workshop

This portion of the product has a graphical, browser-based interface
for all aspects of SQL, from queries to data definition.

Data Workshop

This portion of the product gives you the ability to import data from
text or from XML or Excel spreadsheets, and to export data directly
to text or XML formats.