Oracle Databases on the Web - Table of Contents
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Introduction What's on the CD-ROM Dedication CHAPTER 1—Evolution Of The Internet, The World Wide Web, And Databases Internet Basics Connection Costs Internet Protocols Domains And Location Transparency Internet Applications The World Wide Web Fundamentals Of The World Wide Web World Wide Web Components Accessing The Internet And The World Wide Web What Does The Future Hold? Objects And The Internet The Oracle Approach To Object-Orientation Abstract Data Typing (ADTs) Definition Of Aggregate Objects Abstraction Inheritance Polymorphism Encapsulation
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Oracle Databases on the Web - Table of Contents
Extensibility New Database Design—The ISA Construct Summary
CHAPTER 2—Oracle WebServer Architecture Basic WebServer Architecture The Components Of Oracle’s WebServer Oracle WebServer 1 Architecture Oracle WebServer 2 Architecture Oracle WebServer 3 Architecture Summary
CHAPTER 3—Developing Web Pages Using HTML What Is A Web Page, Anyway? How Are Web Pages Created? The Basics Of Hypertext Markup Language Formatting The Page Background Headers Page Formatting With HTML Lists In HTML HTML Text Styles Special Characters In HTML Link References Linking Images HTML Forms—Soliciting Screen Input Viewing Web Source Code Accessing An HTML File Using WebServer And Netscape Summary HTML References
CHAPTER 4—Installing And Configuring Oracle WebServer Preinstallation Tasks Running The Oracle WebServer Installer Starting The WebServer Installer Installing WebServer Version 1 With Oracle 7.3.2.1 Oracle WebServer 1 Components Installer Prompts Installing WebServer Version 2 Initial Preinstall Tasks Installer Prompts Configuring Oracle WebServer 1 Configuring Oracle WebServer 2 Populating The Oracle Dictionary Installing The Train Demo Testing Your Install WebServer Configuration Issues
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Oracle Databases on the Web - Table of Contents
Handling WebServer Requests Through CGI Or WRB Configuring The Web Listener For CGI Configuring The Web Request Broker For Processing Requests Getting Technical Support Summary
CHAPTER 5—Designing WebServer Applications The Importance Of Web-Based Design Dealing With The Limitations Of The Web Line Speed Client Platform Considerations Designing For Web Access Web Page Scroll Bars Browser Display Web Frames Web Tables Hyperlinks Dynamic Page Generation Clickable Images And Image Maps WebServer Analysis And Design Designing The Application Framework Systems Analysis For WebServer Pages Systems Design For Oracle WebServer Using Audit Logs With Oracle WebServer WebServer 3.0 Log Features Summary
CHAPTER 6—Oracle’s Common Gateway Interface Origins Of CGI Components Of CGI Programming Languages Programs And Scripts Environment Variables Client Documents Image Maps And Forms CGI And Oracle’s Web Request Broker The Webmaster Summary
CHAPTER 7—WebServer’s HTP Utilities HTP/HTF Functional Groupings Print Procedures Structure Procedures Head Procedures Body Procedures
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Oracle Databases on the Web - Table of Contents
Frame Procedures List Procedures Character Format Procedures Physical Format Procedures Form Procedures Table Procedures HTP/HTF Parameters Summary
CHAPTER 8—WebServer’s OWA Utilities Parameter Data Types ProcessedBy OWA Utilities OWA Cookie Procedures And Functions OWA Image Package OWA Init Package OWA Parms Procedures And Functions OWA Pattern Procedures And Functions OWA Text Procedures And Functions OWA Util Procedures Summary
CHAPTER 9—Oracle WebServer And PL/SQL PL/SQL Syntax Structures Declare Section The Begin Section Looping In PL/SQL PL/SQL And Stored Procedures PL/SQL Stored Procedures And Packages Tuning PL/SQL Passing Parameters To Oracle Stored Procedures From The Web Passing Parameters Between PL/SQL Stored Procedures Managing Oracle I/O Using PL/SQL And WebServer Returning A Single Row From An Oracle Database Into A Web Page Returning Lists Of Values From Oracle To A Web Page Exception Handling In WebServer Summary
CHAPTER 10—Managing WebServer Forms And Security Basic Form Functions Data Input Fields Multiple Data Input Fields Checkboxes Radio Buttons Pop-Up Lists Menu Screens Updating The Oracle Database From A Web Page
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Oracle Databases on the Web - Table of Contents
Updating A Single Row Updating Multiple Rows Security And WebServer Forms Oracle Security Oracle Privileges Functions, Stored Procedures, And Packages Assigning Privileges grant Statements Roles Row-Level And Column-Level Security Table Synonyms Session-Level Security Grants And Distributed Oracle Databases Implementing Role-Based Security Creating Key Developer Roles An Implementation Plan For WebServer Security Role Allocation Strategy For WebServer Data-Specific Vs. Application-Specific Security Automatic Conversion To Role-Based Security Auditing Security In A Distributed Oracle Environment Auditing Oracle Role-Based Security Propagating Security Privileges To Many Distributed Oracle Databases The Ten Commandments For Oracle Security Summary
CHAPTER 11—WebServer Navigation And Concurrency Management Interscreen Transfer Interform Communication Database Locking And Concurrency Management WebServer Updates And Concurrency Oracle Database Locking And Granularity Alternative Integrity Mechanisms For WebServer Add A Date-Time Stamp To Each Row WebServer Distributed Database Concurrency Summary
CHAPTER 12—Using Java And LiveHTML With Oracle WebServer Java Development Of Java Java And Portability Object Orientation Of Java Security Of Java Performance Of Java file:///F|/My%20Bookcase/Database/Oracle/Oracle%20Databases%20On%20The%20Web/ewtoc.html (5 of 8)4/03/2005 6:15:08
Oracle Databases on the Web - Table of Contents
Fundamentals Of Java Code Oracle WebServer’s Java Implementation Running Java On The Client Or Server Using PL/SQL With Java Oracle WebServer’s Java Interpreter Accessing Oracle Databases From Java Using PL/SQL Package Wrappers Oracle Database Retrieval By Java Dynamic HTML Generation By WebServer Java Java HTML Examples LiveHTML LiveHTML Syntax Examples Of LiveHTML Summary
CHAPTER 13—Using SQL*Net For WebServer Communication Location Transparency And WebServer Connectivity Oracle Database Domains Intersystem Connectivity With WebServer Internals Of Oracle’s SQL*Net Application Connection With SQL*Net Understanding The SQL*Net Listener Managing SQL*Net Connections Managing Oracle’s Multithreaded Server Managing The Listener Processes Managing Two-Phase Commits (2PCs) Viewing SQL*Net Sessions Summary
CHAPTER 14—Logical Design For WebServer Applications Normalization And Modeling Theory For Oracle Redundancy And Database Design One-To-Many Data Relationships Many-To-Many Data Relationships Recursive Data Relationships Using STAR Schema Design With WebServer Summary
CHAPTER 15—Physical Oracle Design Replication With Oracle Snapshots How To Create Oracle Snapshots Using Triggers To Update Snapshots Using Snapshots To Propagate Subsets Of Master Tables Using Referential Integrity With Oracle Indexes And Oracle Performance file:///F|/My%20Bookcase/Database/Oracle/Oracle%20Databases%20On%20The%20Web/ewtoc.html (6 of 8)4/03/2005 6:15:08
Oracle Databases on the Web - Table of Contents
Tuning Queries With Indexes Concatenated Indexes Oracle Locking Oracle Constraints And Indexes Using Multicolumn Indexes With Oracle How Oracle Chooses Indexes Parallelism And Client/Server Multitasking And Multithreading WebServer Processes SMP Vs. MPP Processing Using Oracle’s Parallel Query Summary
CHAPTER 16—Database Performance And Tuning WebServer Performance Issues The Web Request Broker The PL/SQL Agent Oracle Stored Procedures Pinning WebServer Packages In The SGA Oracle Triggers Deciding When To Use A Trigger Oracle Hashing Oracle Clusters Oracle Parallel Query Summary
CHAPTER 17—Tuning Oracle SQL Tuning Oracle SQL Syntax General Tips For Efficient SQL Using Oracle’s Explain Plan Facility Using Temporary Tables Tuning With The Rule-Based Optimizer Using Hints With The Cost-Based Optimizer Tuning PL/SQL Summary
CHAPTER 18—The Future Of Database Management Oracle Version 8 Oracle Sedona Oracle ConText Oracle Express SQL For Object-Orientation The ISA Relationship The ODMG Object Model The Future Of Hypermedia In Database Management A Return To Centralized Data Experiential Databases
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Oracle Databases on the Web - Table of Contents
Voice Recognition Database Access Summary
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Oracle Databases on the Web:Introduction
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Introduction For the past several years, the Oracle database management system has enjoyed dominance in the worldwide information systems marketplace. Oracle’s excellent reputation has been based on the stability of its Oracle7 Server. In our many years of database and application experience, the Oracle DBMS stands out as being highly reliable and recoverable, two of the main features that information professionals depend on daily. However, until recently, it has been very difficult to get information out of an Oracle database and onto the World Wide Web. Now that you can use Oracle’s WebServer to create Web page front-ends for Oracle databases, developers everywhere are struggling to learn all the facets of WebServer to integrate their databases with the Web. As is the case with any nascent technology, the pragmatic use of Oracle’s WebServer is not yet clear to Oracle developers. In the meantime, we have written Oracle Databases on the Web to simplify the process of using Oracle’s WebServer and explain the development of Web-based Oracle applications in easy-to-understand terms. Interfacing a complex and robust database such as Oracle with the World Wide Web is not a simple task, and there are many hidden pitfalls that must be addressed before it you can easily interface Oracle with Web pages. This book hopes to point out those pitfalls, and the paths you can take to get around them. Oracle Databases on the Web introduces the basic concepts of creating a Web page and interfacing that page to the Oracle database management system. We use Oracle’s
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Oracle Databases on the Web:Introduction
WebServer product to illustrate all the examples in the book, but the focus will be on generic techniques that can be used to interface any Web page with any Unix-based database, using proven Web interface techniques. The most valuable component of this book is a comprehensive set of working examples that can be customized to implement database interfaces to Web pages. You’ll also find techniques in this book for transporting data from the Web page to the PC and from the PC to the Web page. We also explain how LiveHTML can be used to interface with the operating system environment. This book begins by discussing the basics of the World Wide Web and WebServer’s architecture, including a detailed chapter on the installation of WebServer. It then goes on to discuss how to manage WebServer applications, and contains separate detailed chapters on various Oracle utilities that you will need to know about. The book also contains chapters on how to tune Web databases and Web-based SQL. Basically, we’ve tried to include everything you might need to know about WebServer and developing Web-based databases in this book. The Oracle WebServer will become a very hot topic as mainstream IS shops begin to enter the World Wide Web to better service their customers. Oracle Databases on the Web will help to reduce their fear of this technology, and aid Oracle developers in their task of creating robust and functional Web pages that interface with Oracle. The authors welcome feedback and comments. Please address email to: Don Burleson: Bob Papaj:
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Oracle Databases on the Web:What's on the CD-ROM
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What’s on the CD-ROM The companion CD-ROM for Oracle Databases on the Web includes: • A fully functional copy of Oracle WebServer version 2.1! • Complete source code to all examples in the book. • RevealNet’s Oracle Administration Knowledge Base. See the readme files in each folder for acknowledgments, descriptions, copyrights, installation instructions, limitations, and other important information. Requirements Software: Oracle7 Hardware: Platform: Pentium Operating System: Windows NT RAM: 32 MB
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Oracle Databases on the Web:Dedication
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Dedication We dedicate this book to our loving families, and to all our friends who helped support us through the trials and tribulations of writing this tome. Bob Papaj Don Burleson
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
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CHAPTER 1 Evolution Of The Internet, The World Wide Web, And Databases The Information Superhighway began with the development of a wide-area network (WAN) that eventually became the Internet. In its most basic form, the Internet is a world-wide network of subnetworks; it is the backbone for the global transportation of data. The predecessor of the Internet was a Department of Defense project called ARPANET (Advanced Research Projects Administration Network). ARPANET was developed in the early 1970s to assist researchers working in the United States defense industry, as well as a few associates in other countries. ARPANET grew from a network of a few computers in 1971 to over 1,000 by 1984. In 1986, the U.S. National Science Foundation established NSFNET to provide network connections for research institutions. Soon, NSFNET became the new backbone for the Internet. By 1990, ARPANET had dissolved, but the Internet continued to grow via NSFNET. Today, commercial networks run the Internet and have expanded the Internet to provide millions of instantaneously accessible locations to surfers from around the globe.
Internet Basics Despite its overall complexity, the Internet has just a few major components: the
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
physical network, communication protocols, and Internet applications. The physical network of the Internet is comprised of a number of computers linked by routers and cables, working together as if they were a single processor. In this type of wide-area network, communications among the computers is facilitated through Internet languages called protocols. Protocols manage all of the internal transformations that a data file goes through when data is being shipped between processors. Processors use a variety of Internet applications to exchange data. Table 1.1 shows some commonly used Internet applications. Table 1.1Common uses of the Internet. Application
Description
Email
Enables the sending and receiving of text messages.
World Wide Web List Servers
Displays Windows-style pages over the Internet. Broadcast email messages to list subscribers.
Newsgroups
Provide forums for posting subject-oriented email messages.
File Transfer Protocol (FTP) Copies files between sites. Wide-Area Information Servers (WAIS)
Provide more than 500 databases of mainly text-based documents on numerous topics.
Note: While the Internet is very established throughout the Americas and Europe, expansion of the Internet into the remotest parts of the world is constrained by the lack of high-speed phone lines. These high-speed longdistance lines are different from the phone lines we deal with on a daily basis. High-speed phone lines are point-to-point lines where the circuit can be open continuously between connections. Point-to-point lines also have a much greater capacity for carrying data than basic phone lines. The demand for higher capacity lines, similar to those used in WANs, resulted in the production of high-speed, high-volume lines called T1 and T3 service lines. The T3 line is the faster of the two and is used throughout the North American Internet backbone.
Connection Costs Despite the critical nature of the Internet, it’s not totally clear who is responsible for costs associated with installing and maintaining connections among local networks. The cost of connecting a local network to the Internet is commonly paid for by the owner of the local network. The local network owner negotiates a connection with a site already connected to the Internet and pays for a dedicated line that connects the local network to the Internet site. Thanks to the NSFNET project, the National Science Foundation paid for the T3 network backbone in North America. Internet Protocols There are three levels of protocols used by computers to communicate with each other: network, transport, and application. Network protocols coordinate the transmission of information, transport protocols manage the integrity of the data, and application file:///F|/My%20Bookcase/Database/Oracle/Oracle%20Databases%20On%20The%20Web/ch01/001-004.html (2 of 3)4/03/2005 6:15:11
Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
protocols format the data for transmission. The network protocol used by the Internet to get information from one computer to another is called Internet Protocol (IP). Messages delivered by the IP are called packets. The Internet has two transport protocols for coordinating the integrity of network transmissions: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Transport protocols determine whether packets have arrived at their destination, and if so, the protocol assembles the packets in the proper order. As you saw in Table 1.1, there are many applications on the Internet—each of which has their own application protocol. On the Internet, the TCP and IP protocols are often paired together in their usage and jointly referred to as TCP/IP. For the IP to do its job, it needs to identify sites for data transmissions. Under IP, each network and each computer attached to the network has a fixed address. The Internet address is a 32-bit address, partitioned by four 8-bit numbers that identify the computer and its local network. The four bytes (each byte represented by 8 bits) of the address are separated by periods (e.g., 155.222.8.19) and identify either a network number or a host number, depending on the value of the first byte. The first byte (in this case ‘155’) falls within a standardized range of values that will determine the composition of the IP address. In this example, bytes one and two represent the network, and bytes three and four represent the host. The network component is assigned when the local network registers for an Internet connection with the Internet Network Information Center (InterNIC or NIC). NIC gives a range of Internet addresses to the local network’s administrator, who then assigns the numbers to host computers on the local network.
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Domains And Location Transparency Many sites recognize the need to track the locations of remote databases and systems on the Internet while providing “location transparency” to their users and programmers. Location transparency refers to a condition whereby the application requests data as if it were local, yet the data may reside thousands of miles away. Domains are especially important in situations of horizontal partitioning, where data tables with identical names are kept at numerous locations. Domains establish a logical hierarchy of physical locations for any distributed enterprise on the Internet, as shown in Figure 1.1.
Figure 1.1 IP addresses and domain names. The real power of the Internet comes into play when Domain Name Services are used to replace the IP address number with a meaningful mnemonic. For example, the IP address 223.222.45.76 could be given the alias “litterbox,” and Internet users could then Telnet to litterbox without knowing the IP address. Internet Applications
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
Once a backbone had been created for the Internet, software applications were created to allow easy use of the Internet. Some of these applications on the Internet are very common (email, Telnet, and FTP, for example) because they are bundled with the network portion of the Unix operating system—the most common Internet operating system. Other Internet applications (such as Gopher, WAIS, WWW, and Archie) are not a part of the operating system and function as standalone applications. Unfortunately, standalone applications are not always good for sharing data between multiple users because there is no common repository for the data. In order to properly share data with a standalone application, users would have to execute the application on the machine with the data or the data would have to be replicated on many computers. Fortunately, the client/server architecture can help in the goal of data sharing. Network applications work on the client/server model, which distributes the work of one application across two programs, a client and a server. Usually, data is accessed anonymously because it is not necessary to know someone or be known by someone to access data on the Internet. An application is started on the client side that collects details about what is needed by the user, and the client program then proceeds to connect over the network to a server program that controls the information requested. This dialogue between a client and a server is accomplished through application protocol interfaces, which are commonly called APIs. The client-side software formats user requests using the same API as the server. It then dispatches the request by a program that formats the message and transmits it across the network to the server. The server receives the client request, finds the information resource, formats the results in an application protocol, and passes the response to a protocol handler to transmit the requested information back to the client. On the client side, client programs are always ad hoc because a client process is started by a user request. Of course, the server must be ready at all times to respond to a client request, and server programs run continuously, listening for the client requests on their assigned port numbers. Please note that the client/server architecture does not require that the client and the server run on different platforms. Client/server programs can run on the same machine or can run on different machines with heterogeneous operating systems. They can also be defined to support multiple network protocols. Each client program provides a user interface, which may be a character-based interface supporting text only, or a graphical user interface (GUI) supporting text and images like MS Windows. Client programs must execute on an Internet-attached server to access the data repositories connected to the Internet.
The World Wide Web The World Wide Web and the Internet are occasionally interpreted as being one and the same, but they are not. However, the Internet and the Web have been integrated into a powerful behemoth networking system providing links between text, images, and audio information. As we learned earlier, the Internet is nothing more than the physical network of computer hosts. The World Wide Web, on the other hand, is a collection of protocols and standards used to access the vast array of information across the Internet. The World Wide Web uses special applications to retrieve the data on the Internet and can be thought of as residing on top of the basic Internet foundation.
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
The World Wide Web is a very new phenomenon. Since the Web sprang up from its infancy just a few short years ago, it has become the major driving force in worldwide computing. The most fundamental aspect of the World Wide Web is the hypertext link, the procedure for connecting information repositories across the Internet. The hypertext concept, which allows users to access information in a nonlinear fashion, is not new and was developed in the 1940s by an engineer named Vannevar Bush. He visualized users following trails of information in multiple directions and felt this was essential to accommodate the large amounts of data being generated at that time. The actual term hypertext was coined by Ted Nelson in a book he published called Literary Machines (South Bend, Ind., 1981). In this book, Nelson outlined a system called Xanadu, which made use of hypertext links. While Nelson is credited with the original definition, the person most credited with refining hypertext links is Tim Berners-Lee, who in the 1980s was employed at the European Particle Physics Institute (CERN) in Geneva, Switzerland. It was there that Berners-Lee developed a hypertext system used in the physics community to share information. Berners-Lee called the system Enquire-Within-Upon-Everything. This system provided hypertext links consisting of titles, text, and lists of bidirectional-text links.
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Building on their success, Berners-Lee and his associate Robert Caillian compiled the original design documents for a hypertext system as a way to link and access information of various kinds on a web of nodes. The network of links was called the World Wide Web. Contrary to the existing Internet hierarchical systems, which had a rigid path structure for accessing information, the World Wide Web could be accessed without hierarchical access paths. In addition, the design document specified several principles of the Web such as: • Allowing links across multiple machines. • Searching by indexes. • Using a simple protocol to transfer hypertext documents. Hypertext Transfer Protocol (HTTP) later fulfilled this principle. • Using a universal protocol for developing documents. Hypertext Markup Language (HTML) met this specification. • Having the capability to view documents through browser programs. Berners-Lee developed the original hypertext project on a NeXT workstation, and the first hypertext prototype was operational in late 1990. A scientist named Nick Pellow also participated in the project and developed the world’s first Web browser. In May 1991, the project came together and the World Wide Web became readily available to the general public. The Web was greatly assisted in its development by the many discussions that transpired on existing Internet newsgroups, such as alt.hypertext and comp.infosystems.www. An early application of hypertext released in 1987 was HyperCard for the Macintosh.
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
HyperCard enabled users to peruse databases in non linear tracks, very similar to hypertext browsing techniques. As an application, HyperCard grew rapidly in use because it was provided at no charge and was bundled with the Macintosh operating system. HyperCard combined embedded text links with images and sounds, and provided a dazzling display platform for nontextual information. This concept of merging hypertext with multimedia objects became known as hypermedia.
Fundamentals Of The World Wide Web The World Wide Web is best described as a Windows-style data transmission tool that enables a collection of multimedia documents to be connected by hyperlinks. Web technology enables users to click on words and images in a document to access other documents, such as text, images, sounds, and movies. Web applications can be restricted to internal LANs (intranets), or they can be set up to access the full Internet. Most Web development is currently taking place within corporate boundaries on intranets. An intranet is basically a Web application that is only available to users of a closed, subnet of nodes. Many companies remain wary of security issues outside of their protective firewalls (firewalls often act as LAN gateways to the Internet). Intranets can be used for sending and receiving email, distributing and retrieving information, and coordinating departmental and interdepartmental projects. Initially, the Web was designed to transmit text documents, but it became multimediabased with the development of Web browsers. A Web browser provides a GUI front end to the multimedia resources available on the Web. The first Web page accessed on a Web server is called the home page, which generally describes and provides links to all the information retrievable on that server. Clicking on a highlighted box or underlined text opens a link to other Web pages containing additional information. Links can take users to information residing on the same server or on another Internet server located anywhere in the world. World Wide Web Components There are primarily three standard elements that comprise the Web: URLs (Uniform Resource Locators), HTTP (Hypertext Transfer Protocol), and HTML (Hypertext Markup Language). URLs are the Internet addresses that we commonly see (such as http://www.coriolis.com). URLs help to locate data on the Internet by addressing resources across multiple protocols. URLs can identify documents through HTTP, specify email addresses, transfer files through FTP, and access Gopher menus. The format of a URL changes based on the protocol being used. A URL can be broken down into three components: the protocol to be used, the server where the connection will be made, and the path for the file to be accessed. In general, but not universally, the format of the URL is: protocol://servername:port/path Usually the “:port” section is omitted, and the URL will use a default port for that protocol. The port number is an identifier that is assigned to software programs that communicate between networked computers. The server name may be specified in either upper- or lowercase. Also, it can be represented as an IP address or hostname. file:///F|/My%20Bookcase/Database/Oracle/Oracle%20Databases%20On%20The%20Web/ch01/007-010.html (2 of 3)4/03/2005 6:15:12
Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
The IP address is a series of numbers that identify the host and the network location of the host. The hostname is usually synonymous with the domain name. Let’s try an example: spartan.spearsinc.com The domain name in this example is broken down as follows, reading from right to left. The rightmost part of the domain name is referred to as the zone, in this case “com,” which categorizes this as a commercial organization. Table 1.2 shows a list of valid three-character zone names that are commonly used on the Web. There are also two-character zone names that are infrequently used and are geographic identifiers (such as .uk for United Kingdom and .it for Italy). Moving to the left is the string “spearsinc,” which identifies the particular company or organization. Finally, furthest to the left, the hostname “spartan” specifies the lowest-level name of the server. Often, on the Web, you’ll see the hostname specified as “www.” Table 1.2A list of valid three-character zone names. Zone
What It Identifies
edu
Educational institutions
com
Commercial organizations
net
Networked organizations
gov
Government organizations
int
International organizations
mil
Military installations
org
Just about any other group
Note: URLs are almost always case-sensitive. Be sure to enter them exactly as you see them written in the address.
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(Publisher: The Coriolis Group) Author(s): Robert Papaj and Donald K. Burleson ISBN: 1576100995 Publication Date: 02/01/97 Search this book: Go!
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In general, the World Wide Web transfers information across the Internet using the HTTP protocol. In order for HTTP to get information from a server to a client, three steps occur: 1. The client connects to the server. 2. The client sends a request to the server for a specific document. 3. The server responds to the request with a status code, information about the object being sent, and the object itself. The status code usually indicates that the request was successful, but other codes may be returned indicating various errors in transmission. The object information fields can specify an enormous amount of information, including: • • • •
File content type (for example, executable, graphic, or HTML file) Last modification date of the file Document language coding Expiration dates for the validity of the document
The client browser can use the content-type field when determining how to process what was retrieved (for example, a graphic image, a sound, and so on). In addition, browsers can use the last-modified field to reduce repetitive transfers of large images and bitmaps. The most recent transfers are cached within the browser and will not be transferred again when requested unless the last modified field has changed.
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Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
HTTP HTTP has been defined as a “stateless” protocol used to increase data transfer rates. But what does “stateless protocol” mean? It means that HTTP is not required to remember any information about a connection from one request to another. The state of the protocol does not have to be defined internally and can be set within the URL. HTTP can have only one request per connection, which also makes it a “connectionless” protocol. The client-to-server connection is severed after each request is resolved. A new connection must be established to the server for every client request. Retrievals of Web pages that contain many graphic images can take considerable time to complete because a connection must be established for each image. Some browsers, like Netscape and Microsoft Internet Explorer, will transfer multiple documents simultaneously by opening multiple connections; many other browsers transfer documents more slowly, because they are restricted to one open connection at a time, per request. The third leg of the World Wide Web is Hypertext Markup Language (HTML), which is an outgrowth of Standard Generalized Markup Language (SGML). Other markup languages include LaTeX, RTF, and Frame. The markup languages define areas of text by “tagging” them with a specific format for a specific use. Hypertext links can be created between documents with HTML to provide the transport mechanism. This is accomplished by marking documents with code associated with other documents to crisscross the Internet, forming the Web. Accessing The Internet And The World Wide Web In order to access the Internet and the World Wide Web, a computer called a network host must exist and be connected to the Internet. Local area networks (LANs) must connect to one of these network hosts. The local network’s connection point to the Internet is called a router, which is a special computer bridging the LAN to the Internet. A series of dedicated phone lines creates the long-distance part of the Internet’s physical network. Remote computers use dedicated phone lines to connect to LANs that are connected to the Internet.
What Does The Future Hold? Today, the Internet has over 30 million users with thousands of new users being added every day. Ninety-five countries have access to the Internet, and more than 145 countries have access to email. Regulators predict at least a 100 percent rate of growth each year for the Internet. Internet-based systems developed in the 1990s may seem revolutionary, but they are no less revolutionary than the demise of punched cards brought on by the introduction of GUI interfaces in the 1970s and 1980s. A careful study of the evolution of Internet-based online systems establishes a trend line that can give us some insight into the future of distributed Internet systems. While the World Wide Web has added a glossy front-end package to information systems, the internal information architecture has changed very little in the past decade. In fact, file:///F|/My%20Bookcase/Database/Oracle/Oracle%20Databases%20On%20The%20Web/ch01/010-013.html (2 of 3)4/03/2005 6:15:13
Oracle Databases on the Web:Evolution Of The Internet, The World Wide Web, And Databases
the state of online systems has changed relatively little since the 1960s. Online transaction systems continue to process record-oriented information, and if we factor out the convenience of a GUI and a mouse, the core nature of these systems has remained unchanged. However, this does not imply that Internet-based client/server and distributed databases are only a facade. As processors continue to increase in speed and decrease in cost, the next revolution will exploit the inherent power of client/server systems and change the way information systems function, not just how they appear. For example, imagine highspeed processors on everyone’s desk, with each machine having the power of an IBM 3090 mainframe. The client/server component would then become more of a data server than a shared processor, and corporate information could be extracted and manipulated freely within the information domain. The greatest challenges over the next decade will be the management of distributed data. Centralized corporate servers must be built and managed so that a user, regardless of geographical location or computer platform, can instantly access and manipulate data. These new servers will open up new career fields and new jobs, such as the Object Administrator. The widespread acceptance of object technology will dramatically change the complexion of information systems programming. The role of the programmer will change from a craftsman who carefully creates unique programs to that of a program assembler who constructs systems from predefined and pretested code modules. Just as Eli Whitney’s idea of interchangeable parts changed the way that rifles were assembled in the 1700s, object technology will forever change the way computer systems are constructed. Rather than being craftsmen who create a unique work, object-oriented programmers will take on the role of code assemblers, choosing among prewritten and tested code functions and combining them in unique ways.
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