Oracle Discoverer 3i Viewer Configuration Guide for Oracle9i Application Server for Windows Release 3.3.57 A87361-01 |
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# 1
Overview of Oracle Discoverer 3i Viewer

## 1.1 Introduction

Oracle Discoverer 3i Viewer is a business intelligence tool for viewing workbooks created by users of the client/server or web releases of Discoverer Plus (previously known as Discoverer User Edition). Using Oracle Discoverer's easy to use interface via a web browser, users can access and analyze database data.

Oracle Discoverer 3i Viewer is straightforward to set up and maintain. Oracle Discoverer 3i Viewer can be used to integrate database output into your web site and portal and is easily customized to fit in with your web site look and feel, or to build custom Discoverer applications for the web. Oracle Discoverer 3i Viewer is also optimized for performance and designed to minimize network traffic.

This chapter provides an overview of the Oracle Discoverer 3i Viewer architecture, describes the components and illustrates how Oracle Discoverer 3i Viewer works to give data access to users.

## 1.2 Oracle Discoverer 3i Viewer and Oracle9i Application Server

Oracle Discoverer 3i Viewer is installed as part of Oracle9i Application Server. The default installation is to install all Discoverer components on a single machine. However, you can install different components on different machines to improve performance (for more information, refer to Chapter 3, "Installing Oracle Discoverer 3i Viewer on multiple machines".

## 1.3 Oracle Discoverer 3i Viewer in context

Oracle Discoverer 3i Viewer can be used to view workbooks created by Discoverer Plus on client/server or the web. The deployment of Oracle Discoverer 3i Viewer is best understood by looking at its context (see Figure 1-1).

#### Figure 1-1 Oracle Discoverer 3i Viewer components in context

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Oracle Discoverer 3i Viewer is deployed using an Internet computing architecture that sits on top of the existing Discoverer Services.

Oracle Discoverer Services works with the Oracle9i Application Server HTTP listener to provide a robust, scalable deployment platform for the Oracle Discoverer 3i Viewer.

## 1.4 The n- tiered architecture of Oracle Discoverer 3i Viewer

The n-tiers of Discoverer are as follows:

- Client

- HTTP Server

- Discoverer Services

- Database

This architecture takes advantage of the distributed nature of the web environment. While it is possible to install all tiers of Discoverer on the same machine, we recommend distributing your installation over multiple machines to maximize performance.

Important: The Discoverer End User Layer must be in the database before you can configure the client access rights and privileges. You must also first install the Discoverer Administration Edition (v3.1.36 or later).

#### Figure 1-2 The four tiered architecture of Discoverer 3i Viewer

### 1.4.1 First tier - the Client

The first tier of the Discoverer architecture is the client--a user's computer. There is no setup or installation to do on the client machine, nor does this machine need to have access to any database. The only requirement for this computer is that it can run HTML through a web browser (e.g. Microsoft Internet Explorer 4.01 or Netscape Navigator 4.0). By accessing the URL that you (the Discoverer administrator) provide, users can connect and run Oracle Discoverer 3i Viewer to view data.

### 1.4.2 Second tier - the HTTP Server

The second tier of the Discoverer architecture is the HTTP Server tier. The Discoverer 3i Viewer Servlet is installed in the HTTP Server's servlet engine.

Note that in a multiple machine installation, a component from the Discoverer Services tier (the Locator component) is usually installed on the same machine as the HTTP Server tier.

#### 1.4.2.1 What is a Servlet?

A Servlet comprises modules of Java code that run as a server application to answer HTTP requests (hence the name "Servlets", similar to "Applets" that are used on the client side). The Servlet minimizes any client-side processing.

#### 1.4.2.2 What is a Servlet Engine?

A Servlet Engine comes as part of (or as a plug-in to) an HTTP Server and is the environment in which the Servlet runs. The Servlet Engine incorporates a Java Virtual Machine (JVM) and implements the Java Servlet API.

#### 1.4.2.3 What is the Discoverer 3i Viewer Servlet?

The Discoverer 3iViewer Servlet generates HTML pages from HTTP requests using an XML/XSL processor.

The Discoverer 3iViewer Servlet and the XML/XSL Processor are installed in the HTTP Server's servlet engine

### 1.4.3 Third tier - the Discoverer Services

The third tier of the Discoverer architecture is the Discoverer Services. The Discoverer Services consists of three basic components:

- the Locator component

- the Session component

- the Preferences component

The components are installed on one or more application servers. You can install Discoverer Services on one machine or across many machines. The default Oracle9i Application Server installation is a single machine installation. For more information on installing Discoverer Services across multiple machines, see Chapter 3, "Installing Oracle Discoverer 3i Viewer on multiple machines"

In addition, two CORBA (Common Object Request Broker Architecture) components from VisiBroker--an Object Activation Daemon (OAD) and a SmartAgent component--are also installed. These CORBA components are responsible for activating new components and providing a location service whenever the user requests to begin a Discoverer session.

#### 1.4.3.1 Discoverer Services Software Components

The three components that make up the Discoverer Services tier are:

- the Session component.

- the Locator component.

- the Preferences component.

##### 1.4.3.1.1 The Session Component

The Session component provides the link between the client and the database. Once a session is started, it is the client's instance of Discoverer. The Session component contains all of the application logic and performs all of the Discoverer operations such as connecting to the database or opening a workbook.

A machine that has a Session component installed can run multiple concurrent sessions for clients. To increase overall performance, you can install the Session component on many individual machines, and each machine can run multiple concurrent sessions. Distributing the Session component on several machines also improves availability. If one machine is not operating, other machines handle the session requests.

The Session component can run on any server (application or HTTP) in the Discoverer Server configuration as long as the server is a Windows NT machine.

##### 1.4.3.1.2 The Locator Component

The purpose of the Locator is to receive a request for a session from the Servlet (the request is initiated after a URL is sent to the Servlet from the client browser), find the next application server, start a new session, and return a reference for the new session back to the Servlet. Once the Servlet has received this reference, the Servlet and the session communicate with each other and the Locator waits for the next request. The Locator component is installed on the HTTP server. You need only one Locator component on the network for the Discoverer Services.

The Locator component also helps balance the load on the available application servers because it determines which application server will start each requested session. You can specify how the Locator allocates sessions to achieve the best performance.

##### 1.4.3.1.3 The Preferences Component

The Preferences component provides a single location for preference settings for all end users. The Discoverer Services relies on stored preference settings to dictate certain aspects of behavior. You install only one Preferences component for the Oracle Discoverer Services.

Having a single Preferences component is important in a distributed environment where different components can run on different machines. The Preferences component provides consistent preference settings for all components regardless of where they are running.

### 1.4.4 Fourth tier - the database

The fourth tier of Discoverer is the database. The database contains:

- the data users want

- the End User Layer (EUL) that provides an easy to understand view of the data

- the Discoverer workbooks that users can work with to view and analyze the data

You use the Discoverer Administration Edition to create and maintain the EUL.

Note: Before users can use Discoverer 3i Viewer to view data, the database must contain a Discoverer 3.1 EUL. You must create or update the EUL with Oracle Discoverer 3.1.36 or later of the Administration Edition for Windows95/98/NT. If you are currently using Discoverer 3.0.8, you need to upgrade to Discoverer 3.1.36 or later. If you are using Discoverer 3.1.25, you need to install the Discoverer 3.1.36 patch. Discoverer 3.1.36 is Y2K compliant and assures that your EUL and software will work correctly in the year 2000.

### 1.4.5 Discoverer 3i Viewer Components and Hardware

The Discoverer components must each be installed on a server machine. There are three types of server machine that make up the Discoverer architecture:

- the HTTP server machine

- the Application server machine (s)

- the Master Discoverer server machine

#### 1.4.5.1 The HTTP Server

The HTTP Server machine is a machine running HTTP Server software (and the servlet engine) on which you install the Discoverer 3i Viewer Servlet and the Discoverer Services Locator component. You only need one HTTP Server machine as part of your Discoverer environment. If you install the different Discoverer Services software components on a single machine, that machine is both the HTTP Server machine and the Application Server machine.

#### 1.4.5.2 The Application Server machine(s)

The Application Server machine is the machine on which you install the Preferences component and the Session component. You can have one Application Server machine or many Application Server machines as part of your Discoverer environment.

If you install the different Discoverer Services software components on a single machine, that machine is both the Application Server machine and the HTTP Server machine.

If you distribute the different Discoverer Services software components across several machines, you must install the Session component (but not the Preferences component) on every machine. In this scenario, each machine is an Application Server and multiple sessions can be started on each machine. Note that the Preferences component is only installed on one Application Server machine (referred to as the Master Discoverer Server).

#### 1.4.5.3 The Master Discoverer Application Server

If you install the Session component on multiple Application Server machines, you must designate one of those Application Server machine as the Master Discoverer Server. In addition to the Session component, you must also install the Preferences component on the Master Discoverer Server. Note that the Master Discoverer Server is the only machine on which you install the Preferences component.

## 1.5 How Oracle Discoverer 3i Viewer Works

This section describes how Oracle Discoverer 3i Viewer works--from the point when the user launches the browser on the client computer to when data access becomes available. The following figure illustrates the basic process.

### 1.5.1 The Oracle Discoverer 3i Viewer process

#### Figure 1-3 The Discoverer 3i Viewer Process

1. The user launches a Web browser on a client computer and types the URL of the HTTP Server.

2. The Web browser accesses the URL on the HTTP Server.

3. The Discoverer 3i Viewer servlet interprets the HTTP request.

4. The Locator starts a Session component on an Application Server machine and a Discoverer session starts.

5. The Discoverer session requests and receives data from the database.

6. The Discoverer session transmits data to the Discoverer 3i Viewer servlet.

7. The Discoverer 3i Viewer servlet generates an HTML page and sends it to the browser.

### 1.5.2 Oracle Discoverer 3i Viewer Architecture

#### Figure 1-4 The Oracle Discoverer 3i Viewer Architecture

### 1.5.3 Invoking Oracle Discoverer 3i Viewer

Oracle Discoverer 3i Viewer is invoked via a URL from a standard Web browser.

The URL is processed by a Servlet running in the Servlet engine. The Servlet uses the Locator to communicate with the Discoverer Services.

Note: The Discoverer Services can be used by both Oracle Discoverer Plus and Oracle Discoverer 3i Viewer. Therefore the Discoverer Services need only be installed once for both applications.

### 1.5.4 Processing the HTTP request

The Oracle Discoverer 3i Viewer Servlet interprets the HTTP request from the client browser, and makes the necessary calls to the Discoverer Services.

The server response represented in XML is generated by the Servlet and sent to an XML/XSL processor.

The XML/XSL processor combines XML with an XSL configuration file that defines the representation of the User Interface and generates the output (e.g. HTML) to send back to the browser.

The Oracle Discoverer 3i Viewer Servlet is composed of two primary layers - the application logic layer and the presentation logic layer.

The application logic layer manages the handling of the HTTP request, the state of the Discoverer Services, and generates the XML representing the logical state of the Discoverer server and the data for a given client.

The presentation logic layer takes the XML and uses XSL to generate a response in a given format (e.g. HTML, Microsoft Excel, XML etc.). The presentation logic can be customized to alter the appearance of the user interface (by editing XSL files). See Chapter 5, "Customizing Oracle Discoverer 3i Viewer" for details.

### 1.5.5 Scalability and load balancing

The Oracle Discoverer 3i Viewer Servlet and Discoverer Services are automatically installed to run on the Oracle9i Application Server as a single machine installation. However they are designed to be deployed on multiple machines (for more information, refer to Chapter 3, "Installing Oracle Discoverer 3i Viewer on multiple machines"). The Discoverer Services can be replicated by specifying the machines available to Discoverer in a configuration file. Discoverer Services sessions are then started on alternate machines to balance the load.

In this way very large numbers of Discoverer users may be supported, since there is no single bottleneck. Multiple Discoverer sessions can run on a single machine, or can be spread across multiple machines as required.

The Discoverer 3i Viewer servlet can also be distributed.

#### Figure 1-5 Using multiple Discoverer Application Servers for scalability

In Figure 1-5 two HTTP servers are used to spread the load for three browser sessions. There are three server machines, with Discoverer Services running on each. In a real system there would be many users using each HTTP and application server. Discoverer allows you to determine exactly how you want to spread the load across the available machines.

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