LAST UPDATE: 12/13/00
This Learning Module is constantly being updated!
This is the most current version of Learning Module VI; however, the study guide needs to be written (for the independent learner) and
some of the content sections, links, and assessment tools need to be fine-tuned.  (Nothing is wrong, just imperfect!)
Note that the blinking text designates things that I need to work on; the material is not wrong, but can be improved.
(Don't worry, I don't like blinking text, either, so there will not be any in the finished product!)

LEARNING MODULE VI
SURVEY OF PROGRAMMING LANGUAGES
THAT ARE ASSOCIATED WITH THE WEB

        Computer languages are software (translators) that allow a developer to program a computer system; The most common use of computer languages is to write            (1) programs.   Numerous programming languages have been developed to facilitate the translation of the developer's algorithms (procedures for accomplishing tasks) into           (2) language programs that a computer can execute. The following over-simplified survey separates all computer languages into three categories: low, high, and very-high, after which it focuses primarily on examples used for Web applications, especially markup languages, Java, and JavaScript.  (For a little more general survey of programmin languages check out my Learning Module X, of COSC100, Introduction to Computers.)  Independent learners should read the objectives and sequence of presentations, summary, then the Study Guide for this learning module.

The Objectives of this learning module are:

1. to survey the classifications of computer programming languages and focus on those associated with Internet services,
2. to survey the most popular programming languages used to develop Web sites,
3. to define some of the basic software development concepts implemented in Java and JavaScript, and
4. to see how Java and JavaScript can easily be incorporated into Web pages via "cut 'n paste".

The sequence of presentations in this learning module is as follows.  You can click on any link to jump directly to that section.

• 1. PROGRAMMING LANGUAGE LEVELS
• 2. MARKUP LANGUAGES
• 3. JAVA, THE CURRENT "RAGE" IN SOFTWARE DEVELOPMENT (ESPECIALLY FOR THE INTERNET)
• 4. JAVASCRIPT, A VHLL COMPLIMENT TO JAVA
• 5. SUMMARY
• 6. FIGURES FOR LM VI

1. PROGRAMMING LANGUAGE LEVELS:

        A programming language has two primary components (1) a set of built-in language primitives (commands, operations, classes, methods, procedures, functions, etc.) that may be combined into programs and (2) a translator (assembler, compiler, and/or interpreter) that transforms source code (written in the programming language) into object code (machine language equivalent). There are three basic categories of programming languages: (For a comparative examples of these see Comparison of Language Levels in Learning Module X, of COSC100, Introduction to Computers.)

1.1 Low Level Languages are "computer oriented":

1. Low Level Languages = computer oriented languages, i.e. they directly manipulate hardware.
1. Each language is unique to the CPU on which it is implemented and is, therefore, not portable (i.e. not usable on a computer with a different CPU).
2. Each instruction corresponds to a machine operation, part of the "instruction set" characteristic of the          (3).
2. There are two categories of low level languages:
1. Machine Language (ML) uses numeric codes (binary, octal, hex, etc.); non-binary code must be translated into binary code, the only code that can be directly executable by the computer. Writing machine language programs is so tedious, complex, and error prone that it is now virtually never done.However, one must remember that a computer can only execute machine code (i.e. "run" machine language programs); therefore, ALL programs are ultimately translated into machine code, after which they are executed.
2. Assembly Language (AL) uses mnemonic (abbreviated English words) instructions which have a one-to-one correspondence with machine language instructions, i.e. assembly language instructions correspond to specific operations of the CPU. This one-to-one corresponds is what makes assembly language a        (4) (computer oriented) language.  Assemby language must be translated into ML by an assembler.   Assembly language, being machine oriented, is faster and more efficient in the use of hardware than HLL or VHLL.

1. The words and grammar of HLL are English-like. A HLL language is governed by a strict syntax (usable words and set of grammatical rules); if this is standardized, the language is portable (can be used on different computer systems). The majority of software development is done using HLL, and HLL development is a core requirement in computer science degrees.
2. HLL programs reflect the logic and procedures used in a human algorithm. Thus HLL programming is "task-oriented" rather than "machine oriented"; the programmer is able to concentrate on developing task algorithms rather than on how the computer will carry out the instructions. However, the programmer must still specify a complete set of detailed instructions, i.e. code that implements the task        (5).
3. HLL programs are translated into ML by either compilers or interpreters. Most HLL instructions translate into multiple ML instructions.
4. Any HLL can be used to write network applications; however, some make that job much easier than others do.  The two most common ways of writing Web specific programs are:
1. using CGI (Common Gateway Interface), a standard protocol (NOT a programming language) for running external programs from a Web server. Such programs, called "CGI applications" can be written in virtually any computer language (the most suitable is probably Perl).  However, the CGI approach is being superceded by languages specifically designed for writing programs to be run by Web browsers, e.g Java (See the next section.) and JavaScript (See section 1.3.F section 3.)

1. using Java, a purely object oriented, HLL designed to facilitate reliable, platform-independent, distributed processing.  It is a general purpose language useful in writing any type of application; however, it has special capabilities for writing object-oriented programs (covered in section 2.A) that run on networks. The most visible of these capabilities are "applets" (special programs) that can be called directly from within an HTML document. This makes it the "language of choice" for most programmers of network applications. (See section 2.)

        VHLL are very new and are still evolutionary.  Consequently there is disagreement over terminology at present.  The following represent a very brief overview of current concepts and terminology of a huge, diverse subject.

1. VHLL are similar to HLL except they are more sophisticated and easier to learn and use because many powerful primitives are built into the languages. One goal of VHLL is to give nonprogrammers the ability to create simple computer applications.
1. The "power"  and ease of use of these languages arises from the fact that complex tasks can be accomplished with a few simple commands.  To do the same thing using HLL would involve complex algorithm development for which only professional programmers are trained.  These VHLL commands require only that the developer specify "what" tasks are to be performed, not the details of "how" they are performed.
2. However, VHLL are "special purpose languages", (often associated with specific software packages like a DBMS or specific environments like the Web), and thus have have limited range of application, within which they are very powerful. This power, however, removes much control from the hands of the programmer.  Therefore, the power and ease of use of VHLL must be balanced by the sacrifices in control over the processing details and access to computer hardware. As long as the task fits the narrow capabilities of a VHLL, software development proceeds quickly and smoothly.
2. There is little standardization in current VHLL (they are usually intimately associated to a particular type of hardware or software). This results in a lack of portability which has restricted their current popularity. This, however, is changing rapidly.
3. Authoring systems are VHLL designed to allow nonprogrammers to create Multimedia (text, graphics, animation, audio, and video) applications. These have greater potential for developing individualized learning system software.
1. Hypertext Markup Language (HTML) was the original language used to create Web pages; it has been updated via several versions.   HTML is really only a collection of       (6) which, when incerted into regular text, tell a Web browser how to format text, incert multimedia, link to another location, or link to other programs written in VRML, Java, JavaScript, or other languages (CGI applications).  (See section 2.B.)
2. Dynamic HTML (DHTML) is an extension of HTML that  facilitates the enhancement of animation and interactivity of Web pages by providing scripting, cascading style sheets, layering, dynamic fonts, etc.  (See section 2.C.)
3. EXtensible Markup Language (XML) a Web document formating language, is another improvement on HTML.  XML allows new tags to be defined by the developer  for new data types thus dramatically expanding the variety of information that can be handled in a Web page.  XML is "extensible" because, unlike HTML, the ability to define new markup tags makes it virtually unlimited and self-defining.  (See section 2.D.)
4. Synchronized Multimedia Integration Language (SMIL) is an upgrade of HTML that facilitates the synchronization multimedia elements of a streaming Web page enabling its audio, video and graphics elements to be coordinated. (See section 2.E.)
5. (3/19/00)WML (Wireless Markup Language), part of the WAP protocol, is a subset of XML specifically designed to program wireless devices so that they can display the text portions of Web pages.  (Following is from WhatIs) WML (Wireless Markup Language), formerly called HDML (Handheld Devices Markup Language), is a language that allows the text portions of Web pages to be presented on cellular phones and personal digital assistants (PDAs) via wireless access. WML is part of the Wireless Application Protocol (WAP) that is being proposed by several vendors to standards bodies. The Wireless Application Protocol works on top of standard data link protocols, such as GSM, CDMA, and TDMA, and provides a complete set of network communication programs comparable to and supportive of the Internet set of protocols.
1. WML is an open language offered royalty-free. Specifications are available at Phone.com's Web site. According to Phone.com, any programmer with working knowledge of HTML, CGI scripts, and SQL queries should be able to write a presentation layer using WML. A filter program can be written or may be available from a vendor that will translate HTML pages into WML pages.
6. Virtual Reality Modeling Language (VRML) is used to create Web pages with computer generated 3D environments that can be "explored" as if they are the real world. This promotes a highly interactive human-computer interface.
1. VRML allows the developer to describe, in program code, three-dimensional (3D) image sequences and define user interactions with them. Using VRML, you can build a sequence of visual images into Web settings with which a user can interact by viewing, moving, rotating, and otherwise interacting with an apparently 3D environment. For example, you can view a room and use controls to move through the room as you would experience it if you were walking through it in real space.
2. VRML programs can be "plugged into" HTML programs.
3. To view a VRML file, you need a VRML viewer or a browser _______(7), which can be downloaded and installed in the browser.  Examples include Silicon Graphics' Cosmo Player, WebFX, WorldView, and Fountain for the Windows 95 platform. Whurlwind and Voyager are two viewers for the Mac.
4. See the informative article, VRML Brings 3-D Worlds To the Web, from PC Magazine at:
http://www.zdnet.com/pcmag/pctech/content/16/14/ir1614.001.html
5. Twenty clarifying questions (with answers) can be found at:
http://webbuilder.netscape.com/Authoring/Vrml/ss12.html
5. Other web sites, recommended by Yahoo, dealing with VRML are:
• VRML REPOSITORY (http://vrml.sdsc.edu/) is an excellent starting place to explore VRML.
• Instant VRML Home World (http://www.aereal.com/instant/)  - Anyone can create their own VRML home world and have it hosted by Aereal's server for free. Just fill out two HTML forms, and *boom*, instant VRML home world.
• MeshMart VRML (http://www.meshmart.org/vrmlup.htm)  - complete reference source to the new world of Virtual Reality Modeling Language, VRML, including links, reviews and tutorials.
• Proteinman's Top Ten VRML Worlds (http://www.virtpark.com/theme/proteinman/)  - rotating list of the best VRML worlds out there.
4. Scripting languages are designed to help nonprogrammers customize applications or create simple applications, e.g. to "liven up" Web pages.  In general, scripting languages are easier use than high level languages and are ideal for small programs of limited capability or that can reuse and tie together existing high level language programs. The most popular scripting languages include the following
1. JavaScript is VHLL that is a simplified version of Java specifically designed to add dynamic quality to Web pages.  (See section 4, below.)
2. REBOL (Relative Expression-Based Object Language) is a new approach to Web scripting that introduces the idea of a messaging language, one that "provides highly-integrated connectivity (networking) along with context sensitivity (called "dialecting", the ability to create variations, or sub-languages, for domain-specific communication.)". It provides a broad range of approaches to the common challenges of Internet computing.  While designed to be simple and productive for novices, the language extends a new dimension of powerful, practical solutions that facilitate advanced Web development.  Specifically, the languageoffers a significant new approach to the seamless exchange and interpretation of network-based information over a wide variety of computing platforms.  A message can be as simple as a single line or as complex as an entire application.(REBOL's creator on ZDTV, 8 min.)  For more information on REBOL, see the home page of the language at: http://www.rebol.com/
3. Python is simple, high-level interpreted language that combines ideas from ABC, C, Modula-3, and Icon. It bridges the gap between C and shell programming, making it suitable for rapid prototyping and Web scripting. It is object-oriented and supports packages, modules, classes, user-defined exceptions, a good C interface, dynamic loading of C modules and has no arbitrary restrictions.  (This is ZDTV's Leo LaPorte's favorite learning language for beginning programmers.)
4. Tcl (Tool Command Language) is a powerful, extensible, interpreted string processing language for issuing commands to interactive programs.   The extensibility of Tcl means that it can be easily extended through the addition of custom Tcl libraries. It is used for prototyping applications as well as for developing CGI scripts.  It has a peculiar but simple syntax. It may be used as an embedded interpreter in application programs. Tcl has an associated GUI toolkit, Tk, so it is sometimes referred to as Tcl/Tk.
5. Visual Basic and VBScript are are a language duo from Microsoft that rival JavaScript.
1. Visual Basic is specifically designed to quicly and easily develop code that provides interaction between different Microsoft applications, e.g. Word and Access or Internet Explorer.   It is actually more of a "programming environment" in which a graphical user interface is utilized to select and modify "library code" previously written in the BASIC programming language.
2. VBScript is an interpreted script language that is a subset of its Visual Basic programming language.
6. ASP (Active Server Page) is not a programming language, but is called, by Microsoft, "a server-side scripting environment." To create ASP scripts developers typically use the languages VBScript or JScript, both of which are automatically supported by ASP.  ASP and HTML are tightly integrated.  In HTML,        (8) are delimited with brackets; similarly in ASP one uses the <% %> delimiters to define the beginning and end of a script. ASP scripts can be incerted anywhere in an HTML page, and visa versa. One of major assets of ASP is that it facilitates access to SQL databases.  For a nice, introductory tutorial on ASP, access the CNET site,
http://www.builder.com/Programming/ASPIntro/?dd.cn.txt.0701.10

2. MARKUP LANGUAGES:

      Markup languages are VHLL authoring systems that allow developers to "mark up" text with tags that format it, incorporate multimedia into it and create hyperlinks in it.  The most commonly known example is HTML, in which this learning module is written, but it is being superceded by newer more sophisticated languages.

1. Standard General Markup Language (SGML) is a generic markup language for representing documents..  It is not a language itself but a "metalanguage" that specifies how a markup language like HTML, DHTML, XML, etc. will work.  It is used to specify the tag set of the markup language as well as it's syntax.
1. The foundation of SGML is the idea that a document has a format and components which can be specified independently of how that document will be displayed, for example, by a           (9). When displayed, the actual appearance of such a document will depend on the output device and style preferences.
2. A document written in a SGML-based language uses a Document Type Definition (DTD) file that specifies the          (10), embedded within it.
3. Because SGML is an international (ISO) standard, based on simple ASCII text, that is platform-independent, portable to all types of hardware, and adaptable to various I/O formats, it has the follownig  advantages:
1.                                       (11).  Document design is independent of display devices and application programs, so a document can be created by considering its inherent format without worrying about how it will appear when displayed.  Therefore, display devices and application programs can be changed knowing that these documents can always be displayed, and that they will retain their basic format and structure.  Also, organizationscan confidently write their documents in SGML-based languages and store their output without being limited to a specific vendor.
2.                        (12).   Documents can be accessed from different computer environment because the document type definition (DTD), is independent of both the hardware on which the documents are displayed and the software from which they are accessed.
3.             (13). The separation of content from its presentation allows fordifferentoutput formats like  HTML, text, CD-ROM, etc.  Text can beeasily be adapted for the type of display device, e.g. the computer monitor, or TV.
4.                              (14). SGML is a core data standard that enables SGML-aware applications to interact and share data seamlessly.
2. Hypertext Markup Language (HTML) is the VHLL that is currently used to create                     (15).  It is based on SGML, i.e. HTML implements, with its tags and syntax, the specifications defined in SGML.
1. HTML itself is the set of customizable "markup" tags that are inserted into HTML document govern its format, multimedia content, and hyperlinks.  Such documents can be displayed by any HTML viewer but they are normally viewed using a Web browser.
2. HTML is a programming language in that an HTML document is a program that, when "run" by a browser, displays its text as hypermedia (multimedia with hyperlinks).
3. The "language" HTML is really only a collection of predefined tags which, when incerted into regular text, tell a Web browser how to:
1. format the document and its text,
2. incorporate                     (16), i.e. incert a graphic image, video sequence, or sound clip into the displayed document,
3. link to other locations, in the same document, in another Web page, or even on another computer (server), or
4. link to other programs written in VRML, Java, JavaScript, or other languages (called CGI applications).
4. Raggett's 10 Minute Guide to HTML, found at http://www.w3.org/MarkUp/Guide/ is the introduction provided by HTML's official sponsor the World Wide Web Consortium (WC3).   This nice little guide and its extension, Adding a touch of style, is considered part of this Learning module, so if you have not read it during the lab sessions, be sure to do so now. It's content is assessable on preassessments as well as assessments.
5. More information:
1. Twenty clarifying questions on HTML (with answers) can be found at:
http://webbuilder.netscape.com/Authoring/Html40/?st.bl.advtech..html4
1. An excellent starting point for further information on HTML is CNET's Spotlight on HTML at
http://home.cnet.com/category/0-3880.html.

3. Dynamic HTML (DHTML) is a collective term for a combination of new HTML tags and options, style sheets, and programming that will let you create Web pages more animated and interactive than standard HTML. Simple examples of DHTML pages would include (1) having the color of a text heading change when a user passes a mouse over it or (2) allowing a user to "drag and drop" an image from one page to another. DHTML is supposedly a simpler way of adding animation and interactivity to Web pages than Java and JavaScript, the popular way to do this now. (From W3C Stylesheet page, http://www.w3.org/Style/: Dynamic HTML is a term used to describe HTML pages with dynamic content. CSS is one of three components in dynamic HTML; the other two are HTML itself and JavaScript (which is being standardized under the name EcmaScript).  The three components are glued together with DOM, the Document Object Model. Dynamic HTML is still in its infancy and current implementations are experimental. ) Some of the more important capabilities of DHTML include:
1. a scripted, object-oriented view of a Web page and its elements.  For example, each heading on a page can treated as a distinct object, i.e. it can be named, given attributes of text style and color.  More importantly, such objects can be addressed, by name, in  "scripts" (small progams) placed within the DHTML. These scripted objects can change as the result of a specified event (e.g. a mouse passing over it or being clicked or a time interval elapsing).  Also, an image object can be dragged and dropped from one page location to another.
2. cascading style sheets allows the developer to specify different style sheets or style statements with predefined levels of precedence within a page or group of related pages. The style can be scripted to change as a result of user interaction causing the appearance of the Web page to change.  "Cascading" means that a page can have multiple layers of style sheets (e.g. a style sheet within a style sheet within a style sheet, etc.). A new style sheet may vary one or more objects in the style sheet above it.
3. layering allows existing content objects to be replaced by or superimpose with new content. Layers can be programmed to appear as part of a timed presentation or as the result of user interaction.
4. Dynamic fonts, a feature introduced in Netscape Communicator, allows Web page designers to include font files containing specific font styles, sizes, and colors as part of a Web page and to have these fonts downloaded with the page. Therefore, font choice is no longer dependent on the browser itself.
For more information on DHTML, See the informative article, DHTML, More Client, Less Server, from PC Magazine at: http://www.zdnet.com/pcmag/issues/1613/pcmg0066.htm
4. Extensible Markup Language (XML), a platform-independent Web document formatting language, is another improvement on HTML.  XML is "extensible" because, unlike HTML, the ability to define new markup tags makes it virtually unlimited and self-defining.  XML allows the developer to define new tags  specifically for new data types thus dramatically expanding the variety of customized data that can be handled in a Web page.   In fact, it has been said that "XML is to data what HTML is to text", but since text is a specific form of data, XML is a more general markup language than HTML.   (It may compete with DHTML to be the successor of HTML, or it may, at least in the near future, be used in conjunction with DHTML to complement HTML in Web applications.)
1. Instead of using only predefined tags (like HTML does) to format a page and insert MIME files in it,  XML allows tags to be defined by the developer of the XML document. Thus, tags for virtually any data type (e.g. product, quantity, and price) can be used for specific applications (like an online shopping site), allowing Web pages to function like database management systems.
2. XML is a subset of SGML (See section A, above.) whereas HTML is a document type of SGML.
3. XML is             (17) because, unlike HTML, the markup symbols are unlimited and self-defining.
4. XML is being supported by the United Nations as a premier standard for e-business.
5. More information:
1. An excellent introduction to XML can be found in the ACM student magazine Crossroads.
2. For focused questions and answers on essential XML concepts see:
http://webbuilder.netscape.com/Authoring/Xml20/?st.bl.advtech..xml20
1. For an introduction to XML try the informative article from SunWorld at:
http://www.sunworld.com/swol-06-1999/swol-06-itarchitect.html?0615a
5. SMIL (Synchronized Multimedia Integration Language), pronounced "smile", was first released in the Fall, 1997.  It is designed to facilitate the definition of and synchronization of streaming multimedia elements (video, sound, still images).  Using HTML, each multimedia element on the Web page is distinct so complex programming is necessary to coordinate them.  SMIL makes it possible to separately transmit multiple video, image and sound files but coordinate their association on a Web page.  Each multimedia object is identified with a unique (URL) thus allowing their coordination and reuse.
1. SMIL tagss are  similar to those those of HTML so the language can be used anywhere that HTML is used.   A presentation can be described using only three XML elements.
2. SMIL  supports multimedia streaming protocols such as RTSP.
3. SMIL also lets the "producer" store a multimedia object in multiple "versions", each with a different size so that a smaller version can be transmitted to users who have low bandwidth channels.  The bandwidth of the user can be determined and the version most appropriate for that is automatically transmitted using a switch statement.  SMIL also makes it possible to have multiple language versions of soundtracks on a Web page.

3. JAVA, THE CURRENT "RAGE" IN SOFTWARE DEVELOPMENT (ESPECIALLY FOR THE INTERNET):

       Java is a high-level, general purpose, platform independent, purely object-oriented programming language that is designed for efficient software development for a distributed (networked) computer environment. It was created at Sun Microsystems to develop advanced software for consumer electronics. C++ was originally chosen for this project, but the code often required extensive debugging and was difficult to maintain. Realizing that a completely new language was needed, the development team started with C++ but removed many of its problematic and seldom-used features and added primitives for distributed computing and other modern features. The result was Java, familiar (because of its syntactic similarities to C++) and simple (at least when compared to C++!). Because of its special capabilities for network programming, it has become, since about 1995, "the" development language for Internet and intranet applications.

1. Java is object-oriented, which means that, software developers think in terms of "objects" which have a "state" (definded by its "attributes") and "behavior"( defined by its "methods").  For example, consider a window on a computer screen; its attributes would include its location, its size, whether or not it scrolls, etc and some of its methods would would be subprograms that define its abililty to be opened or closed, moved, resized, etc.  In other words object-oriented programing (OOP) is a human-oriented view of programming rather than a computer-oriented view. Characteristic of OOP include:
1. Similar objects can take advantage of being part of the same "class" of objects.  A class is an abstract "template" for creating objects, but an object is an "instance" of a class.  For example the idea of a computer window would be a class, but the actual window which contains the text you are reading is an "instance" of the class window.  Each instance of the class window would have different values of          (18) (location, size, etc.) but all would share the same       (19) (movable, resizeable, etc.)
2. Perhaps the greatest asset of OOP is its built-in facilities for reusing code, making software development more efficient.  This can be accomplished three basic ways:
1. Classes can inherit the code (attributes and/or methods) from a parent class (or superclass).  Inheritance is used to "derive a subclass from a superclass", i.e. the subclass inherits the attributes and methods of the superclass and new attributes and methods can be added thus distinguishing the subclass.  Thus the subclass is a special case of the superclass and one can describe inheritance as an "IsA" relationship between classes, e.g. a the Car class could be a subclass of a        (20) class or a "car IsA        (20)".
2. Classes can contain other classes, i.e. incorporate code already written for other classes.  Containership (the proper word is "aggregation") is called a "HasA" relationship between the classes, the Car class would be defined with an engine as an     (21), but if Engine were a class itself, one would say that the Car class HasA Engine class, i.e. the Engine class is contained within the Car class.
3. Methods within a class can make use of other classes as well.  This is called the "UsesA" relationship between classes.  For example a method called "drive" of the Car class might be written using the class SteeringWheel (must be one word), in which case one would say the Car class UsesA SteeringWheel class.
3. The methods of a class are "mini-programs" that define the class's behaviors, one method for each behavior. The logic of method can be completely defined using only three control structures: (They are called "control" structures because they are used to control the flow of execution of the method.)  They are:
1. sequence, the default execution is one instruction after another unless modified by selection or repetition constructs,
2. selection (IF-THE-ELSE; also called IF-ELSE) allows a logical expression to select one of two alternative blocks of code to execute,
3. repetition (WHILE, or FOR loops or recursion) allows a logical expression to govern the repetition of a block of code.
Note that, although sturctured control structures are essential to OOP languages, there are languages that use the same sturctures (e.g. C, Pascal, etc.) but which are not OOP languages, i.e. they do not have the features of section A.b, above.
4. Objects are thought of as "nouns" that a user might relate to rather than the traditional procedural "verbs" which are used as method names.
2. The language is unusual among programming languages in that it is designed to facilitate the creation of two types of software, "applications", "applets", and "servlets".
1. Applications are stand-alone programs in the traditional sense but are based purely on object oriented technology.
2. Applets are a unique innovation of Java.  They are "miniature applications" that are specifically designed to be called from within HTML documents.
1. They must be downloaded from a server in order to be executed on a client. (See Figure SPL-1.)  However they are never stored on the client and are nomrally  prevented from accessing files on the client, although this restriction is being relaxed in new versions of Java.
2. Applets are typically used to add animations or user interactiviey to a Web page.
3. Servlets are an even newer concept unique to Java.  Servlets also "miniprograms" but, unlike applets, they are not downloaded in order to be executed on a client; instead, servlets are executed on the server and, if necessary, its output is downloaded to a client.
3. Java’s most innovative features are its facilities for distributed computing. These include:
1.                  (22) (described above)
2. unique set of Internet/intranet primitives from which programs can be constructed, e.g. class libraries (reusable subprograms) for TCP/IP protocols. Java code can access objects (other programs) across the Internet/intranet via URLs as easily as on a local file system. Java 1.1 and higher also has built-in ability to access objects on remote computers.
3. built in facilities for handling security problems inherent in distributed systems. This makes it easier to develop reliable, virus-free, tamper-free systems. The reliability goal means it was designed to be secure (hacker resistant) and robust (bug resistant). Being robust ensures that a Java instruction can not contain the address of data storage in another program or in the operating system itself, because errors in such instructions will cause the program (or even the operating system itself) to  "crash." The Java virtual machine makes a number of checks on each object to ensure integrity.
4. Java is designed to be run on the "Java Virtual Machine" (JVM), an "abstract computer architecture" that is modelled in the Java programming environment. The Java compiler translates the Java source code (files with a .java extension)into architecture-neutral bytecode (files with a .class extension). (See Figure SPL-3.) Bytecode (a sequence of 8 bit codes) can be executed by a Java interpreter or just in time compiler (JIT) to deliver output to the user.  This implements a "three-tier client server architecture" where the        (23) is the middleware level between source code and object code, i.e. the Java source code is compiled into       (23) that is, in turn, automatically translated,  when it is downloaded, into the       (24) code of the particular CPU.
1. bytecode is designed to be both easy to interpret on any machine and easily translated (by a JIT)  into native machine code at load time.
2. Since the software developer need write only one source code program, this gives Java applications their "platform independence". (This means tha a Java program does not depend on the                             nor          (25) so a program will run on any computer system that has a  (26). Java bytecode can be run anywhere in a network on any server or any client that has a Java virtual machine.)  This is the origin of Sun Microsystem’s Java Slogan:

         which has been expanded, with the advent of the Java component model, Java Beans, to read:

Write Once, run anywhere, reuse everywhere!

 
On Wednesday, Nov. 18, 1998, Sun won a stunning court decision against Microsoft requiring that Microsoft stop its efforts to "pollute" Java in order to destroy its platform independence!  "It's an unqualified victory for Sun," said Rich Gray, a partner at Bergeson, Eliopoulos, Grady & Gray in San Jose, California. (Mr. Gray is not retained by either side.) "This decision gives complete credence to the government's theory that Microsoft has engaged in anticompetitive activities to undercut Java, the most important cross-platform technology." Details can be found here.  A related story can be found on Microsoft's War on Java.
5. Java is the heart of the revolutionary NC (network computer); See Figure SPL/3.
6. For more information on Java see the following:
1. The home of Java is at Sun Microsystems' Java page, http://java.sun.com/.
2. An incredible source of links to Java sites, applets you can download, tutorials on Java, etc is Gamelan at http://www.gamelan.com/.
3. Excellent introductory tutorials on Java are found on IBM's Web site at http://www.ibm.com/java/education/intro/courseoptions.htm
7. EXAMPLES:
1. The following news ticker from 7@m News on the Net  can be added to a Web page by accessing: http://www.7am.com/

You can find the code responsible for calling and displaying the output of this applet by selecting Page Source From the View menu in Navigator.  The code is:
 
<applet CODE="sevenAMNewsTicker.class" CODEBASE="http://www.7am.com/java" WIDTH=450 HEIGHT=15>
<br><param NAME="channels" VALUE="+WORLDnews +CHRISTIANnews +USAnews +SPORTSnews">
<br><param NAME="target" VALUE="_blank">
<br></applet></ol>


It might be easier to distinguish in a page by itself; click here.

4. JAVASCRIPT, A VHLL COMPLIMENT TO JAVA: (See handout, "Spotlight on JavaScript."):

1. JavaScript is a cross-platform, object-based scripting language for both client and server applications.
2. JavaScript is desinged to be embedded directly in HTML. It allows you to create dynamic, interactive Web-based applications that run completely within a Web browser; you don't have to write any programs that run on the Web server, like you must do with CGI scripts, or must be downloaded fromt the server like Java     (27). JavaScript can be embedded in an HTML document four different ways:
1. as statements and functions written within the HTML <SCRIPT> tag,
2. by specifying a file as the JavaScript source,
3. by specifying a JavaScript expression as the value of an HTML attribute, and
4. as event handlers within certain other HTML tags (mostly form elements)
3. JavaScript is not a "native" feature of the Java environment, i.e. it was not developed by Sun or any standards organization as part of or an extension of Java itself.  The origin of JavaScript was "LiveScript", a scripting language, developed by Netscape, for writing scripts that could be inserted directly into HTML code in order to add functionality to Web pages. However, Netscape renamed Livescript as "JavaScript", and, in cooperation with Sun, Netscape is integrating JavaScript into the Java environment as THE scripting language of HTML.
4. JavaScript is a "work in progress".  The latest version of the language, JavaScript 1.2, is supported by Netscape Navigator 4 and Internet Explorer 4.   The first standard version (JavaScript 1.1) was named ECMAScript.  The new features of JavaScript 1.2 are likely to be embodied in a later ECMAScript standard release
5. JavaScript is object-based because it has very limited OOP features. It provides built-in objects but it does not have the capability to define new classes, and it has limited inheritance (via the prototype mechanism). However, being a "work-in-progress", it might have such features incorporated later.
1. The syntax of JavaScrip is identical to that of Java for  features that are common to the two lanaguages. However, JavaScript and Java are fundamentally different!  (See the handout,JavaScript Overview.)
2. Visual JavaScript, written entirely in Java, is a new visual IDE (integrated development environment) tool that lets a company's software developers rapidly build Crossware applications (applications that run across Intranets and Extranets) without writing software code.
3. JavaScript is a simpler than Java and is used for different purposes. It can only be embedded directly in               (28), so can not run as a stand alone application like Java programs can.  On the other hand, it is more flexible and easier to use for simple tasks like animation. However, although you can write reasonably robust and complete Web applications using JavaScript alone, JavaScript is not a substitute for Java. In fact, JavaScript is a good client-side complement to Java; using the two together allows you to create more complex applications than are possible with JavaScript alone.
6. EXAMPLES:
1. For two illustrative examples of JavaScript click here.  You can see the JavaScript by selecting Page Source from the View menu.
2. Another "fun JavaScript", found by a student, Clint Malone, can be found here.
7. JavaScript, Java, HTML/DHTML complement (or should complement) each other.  See the article, by the "ScriptBoy", Danny Goodman called Java vs. JavaScript -- The Impact of Dynamic HTML.   A provocative article on the importance of using learning JavaScript, learn JavaScirpt...now! by Dan Shafer is also worth reading.
8. Other Web sites concerning JavaScript include:
1. C|NET's Web development site, Builder.com found at: http://builder.cnet.com/Programming/JsSpotlight/?st.bl.pr.pr4.feat.1245.
2. An introductory tutorial on JavaScript, by C|NET, can be accessed at http://builder.cnet.com/Programming/Javascript/?st.bl.prog.feat.

5. SUMMARY:

1. In general, programming languages are software development environments that consist of (1) a set of language primatives (keywords and specified syntax) and (2) a translator (assembler, compiler, or interpreter) that converts source code (written in with programming language primatives) into object code (binary machine language).  Programming languages are classified in three categories:
1. Low level languages, which are computer oriented, are used to create programs that have a one-to-one correspondence between their statements and the machine language statements based on the instruction set of the CPU.  Low level language programs make efficient use of the CPU and memory, but, because they are tedious and difficult to write correctly, are inefficient from the standpoint of developer time and effort.
1. machine language which are numeric, and
2. assembly language which utilizes mnemonic keywords.  Assembly language programs are translated into object code by assemblers.
Low level languages are not useful in Internet applications, particularly Web site development.
2. High level languages (HLL), which are task oriented, facilitate the coding of algorithms.  These languages are the primary tools of computer scientists and are therefore a key component of Computer Science curricula.  HLL are mainly used in Web development as CGI applications or, in the case of Java, for writting applets.
3. Very high level languages (VHLL), which are human oriented, are designed to allow non-programmers develop customized software.  They are very powerful within the limited domain of their application.  There is a wide range categories of VHLL but the two most useful in Web development are:
1. Authoring languages like markup languages (HTML, DHTML, XML) and modelling languages (VRML) are use to create Web pages and other hypermedia documents.
2. Scripting languages like JavaScript are used to write miniture programs that can be included within Web pages providing animation and interactivity.
2. Markup languages are VHLL used to create documents that are hypermedia when viewed by a compatible viewer such as a browser.  They are called "markup" languages because they consist of ''tags" that are inserted to pure ASCII text in order to format it and create hyperlinks.
1. SGML is the metalanguage which defines the characteristics of all the following markup languages.
2. HTML was the original Web development languages.  It has evolved through several versions and will probably be superceded by the following languages.
3. DHTML, which stands for DYNAMIC HTML, adds animation, interactivity, and other user-friendly features to HTML.
4. XML is an extensible markup language that allows developers to define their own tags thus making it possible to specify an unlimited variety of user defined data types.
3. Java is a general purpose, platform independent, purely object-oriented HLL that has primatives for distributed computing and other modern facilities.
1. Object oriented languages are based on reusable, abstract templates called classes; they normally contain attributes which specify the state of an object and methods which define the behavior of that object.
1. To create actual objects, the abstract classes are instantiated by giving specific values to its attributes.  Such objects are more accurately called "instances" of the class.
2. The following three fundamental object-oriented relationships between different classes facilitate reuability of code.
1. Inheritance implements the "IsA" relationship between a parent class and a child class; the child inherits the non-private attributes and methods of the parent.
2. Aggregation implements the "HasA" relationship where a class that contains another class as the type of one or more of its attributes, i.e. the container class has an attribute defined by another class.
3. Dependency implements the "UseA" relationship when a method contains other classes for its parameters, local variables, or return type of the method.
2. Java programs can be standard, stand-alone applications or applets, a unique new way of allowing clients (e.g. a browser) to download and run these miniprograms" and have their output displayed witin the client output (e.g. the applet output will appear in the Web page itself).  Servlets are an even newer concept where the miniprogram is not downloaded; instead, it is executed on the server and, if necessary, its output is downloaded to a client.
4. JavaScript is a VHLL scripting compliment to Java which has the same language syntax; however, it does not have the object-oriented facility of inheritance, so it is called an "object-based" language rather than an "object-oriented" language.  Also, unlike Java, JavaScript programs, called "scripts", are coded directly within an HTML document or within a document written with another markup language.