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LIS650 lecture 6 javascript, http and apache

Thomas Krichel 2004-10-30. LIS650 lecture 6 javascript, http and apache. today. javascript http semantic web apache introduction. the <script>. <script> is an element that calls a script.

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LIS650 lecture 6 javascript, http and apache

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  1. Thomas Krichel 2004-10-30 LIS650 lecture 6javascript, http and apache

  2. today • javascript • http • semantic web • apache introduction

  3. the <script> • <script> is an element that calls a script. • It requires a "type" attribute that gives the type of the script language. e.g. type="text/javascript". • It takes the "src" argument that gives a URI where the script can be found. Such a script is called an external script. • It takes a "defer" attribute. If set as defer="1" you tell the user agent that the script will generate no output. This helps the user agent in that case.

  4. example <script type="text/javascript"> document.write("hello, world"); </script> • Interestingly enough, you can place this script in the head or the body. • This is an example of an automated script. The user has to do nothing to get the script to run. • You can also trigger a script. To do that, we have to study some more HTML attributes. We will do that later.

  5. external script • You can also create an external file, say hello.js with the line document.write("hello, world"); • Then you can call it up in the html file <script type="text/javascript" src="hello.js"/>

  6. default script language • You should set the default scripting language used in the document using the <meta> element in the <head> • <meta http-equiv="content-script-type" content="text/javascript"/> • If you don't the validator does not complain, but I don't see other ways to specify the language.

  7. Javascript history • A programming language that was developed by Netscape for their browser in 1995. • To counter, Mickeysoft developed Jscript. • It has been standardized by the European Computer Manufacturers Association as ECMA 262.

  8. principal features • It contains instructions for a user agent to execute. Javascript is not run by the server. • It resembles Java, but not the same language. • It is an object-oriented language.

  9. object • In an object-oriented language, an object is the prime focus of attention. • An object has properties and methods. • Example from real life. Let a bus be an object. • “color” of the bus is a property • “move to next station” is a method

  10. objects in javascript • Properties are accessed by object_name.property_name • Methods are accessed by object_name.method_name() • where object_name is the name of an object, property_name is the name of a property and method_name() is the name of an object. Note the use of the dot and the parenthesis.

  11. Example • Syntax rules • Comments are started with // and go to the end of the line. • Instructions are terminated with semicolon • Example // create a new object called bus new bus = Object(); // paint it white --- set a property bus.color = ‘white’; // move to next stop --- apply a method bus.movetonextstop();

  12. event attributes • Event attributes can be given to elements (like any attribute, really) • The name of the attributes gives a certain event that could happen to the element. • The value of the event attribute is the script to be executed when the event occurs on the element that has the event attribute. • Example <p onmouseover="stink">Cow shit is ... </p> as the user moves the mouse over the paragraph, the browser fires up an imaginary script called stink that makes it start to stink.

  13. core event attributes I • "onclick" occurs when the pointing device button is clicked over an element. • "ondblclick" occurs when the pointing device button is double clicked over an element. • "onmousedown" occurs when the pointing device button is pressed over an element. • "onmouseup" occurs when the pointing device button is released over an element. • "onmouseover" occurs when the pointing device is moved onto an element.

  14. core events attributes II • "onmousemove" occurs when the pointing device is moved while it is over an element. • "onmouseout" occurs when the pointing device is moved away from an element. • "onkeypress" occurs when a key is pressed and released over an element. • "onkeydown" occurs when a key is pressed down over an element. • "onkeyup" occurs when a key is released over an element.

  15. special event attributes • "onfocus" occurs when an element receives focus either by the pointing device or by tabbing navigation. This attribute may only be used with the <a> element, and some form elements that we have not covered. • "onblur" occurs when an element loses focus either by the pointing device or by tabbing navigation. It may be used with the same elements as onfocus.

  16. more special event attributes • "onsubmit" occurs when a form is submitted. It only applies to the <form> element. • "onreset" occurs when a form is reset. It only applies to the <form> element. • some more are only used with other form elements... • Let us look at some examples

  17. two stupid examples <html><head><title>javascript test</title> <meta http-equiv="content-script-type" content="text/javascript"/></head> <body><p onmouseover="alert('Today is '+Date());" >time</p><hr/> <p onmouseover= "document.write('not funny')">joke</p> <p></body></html>

  18. An even more silly example <html><head><title>Bush in the bush</title> <meta http-equiv="content-script-type" content= "text/javascript"/><script type="text/javascript"> prbu=new Image(); prbu.src="bush.jpg"; natb=new Image(); natb.src="natgeo.jpg"; </script></head><body><h4>Bush in the bush</h4><div><img id="bush" src="bush.jpg" onmouseover="document.bush.src=natb.src" onmouseout="document.bush.src=prbu.src" alt="bush in the bush"/></div></body></html>

  19. http • Stands for the hypertext transfer protocol. This is the most important application layer protocol on the Internet today, because it provides the foundation for the world wide web. • defined in Fielding, Roy T., James Gettys, Jeffrey C. Mogul, Paul J. Leach, Tim Berners-Lee ``Hypertext Transfer Protocol -- HTTP/1.1'' (1999), RFC 2616

  20. history • 1990: version 0.9 allows for transfer of raw data. • 1996: rfc1945 defines version 1.0. by adding attribute:value headers. • 1999: rfc 2616 • adds support for • hierarchical proxies • caching, • virtual hosts and some • Support for persistent connections • is more stringent.

  21. http resource identification • identification of resources is assumed through Uniform Resource Identifiers (URI). • As far as http is concerned, URIs are string. • http can use ``absolute'' and ``relative'' URIs. • A URL is a special case of a URI.

  22. rfc about http An application-level protocol for distributed, collaborative, hypermedia information systems. … HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, including those supported by the SMTP, NNTP, FTP, Gopher, and WAIS protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications.

  23. http assumes transport • http assumes that there is a reliable way to transport data from one host on the Internet to another one. • All http requests and responses are separate TCP connections. The default is TCP port 80, but other ports can be used.

  24. use of other standards • http shares the same registry as the MIME multimedia email extensions. It is based at the IANA, at http://www.isi.edu/innotes/iana/ assignments/media-types/media-types • The default character set is ISO-8859-1.

  25. Absolute http URL • the absolute http URL is http://host[:port][[abs_path][?query]] • If abs_path is empty, it is /. • The scheme name "http" and the host name are case-insensitive. • Characters other than those in the ``reserved'' and ``unsafe'' sets of RFC 2396 are equivalent to their ``%HEX HEX'' encoding. • optional components are in [ ]

  26. http messages • There are two types of messages. • Requests are sent form the client to the server. • Responses are sent from the server to the client. • The generic format is the same as for email messages: • start line • message headers • empty line • body • Empty lines before the start line are ignored. • The request's start line is called the request-line. • The response start line is called the status-line.

  27. overall operation server side • Server sends response, required items are • status line • protocol version • success or error code • optional items are • server information • body

  28. overall operation: client side Client sends request, required items are • method • request URI • protocol version • optional items are • request modifiers • client information • Let us now look at different methods

  29. GET and HEAD method • The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI. If the Request-URI refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not the source text of the process. • The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response.

  30. Conditional & partial GET • The semantics of the GET method change to a ``conditional GET'' if the request message includes an • If-Modified-Since • If-Unmodified-Since • If-Match • If-None-Match • If-Range header • The semantics of the GET method change to a ``partial GET'' if the request message includes a Range header field. A partial GET requests that only part of the entity be transferred

  31. The POST method • The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the following functions: • Annotation of existing resources; • Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles; • Providing a block of data, such as the result of submitting a form, to a data-handling process; • Extending a database through an append operation.

  32. PUT and DELETE methods • The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an already existing resource, the enclosed entity should be considered as a modified version of the one residing on the origin server. • The DELETE method requests that the origin server delete the resource identified by the Request-URI.

  33. The request headers • Accept: Accept-Charset: • Accept-Encoding: Accept-Language: • Authorization: Expect: • From: Host: • If-Match: If-Modified-Since: • If-None-Match: If-Range: • If-Unmodified-Since: Max-Forwards: • Proxy-Authorization: Range: • Referer: TE: • User-Agent:

  34. The status line • The status line is a set of lines that are of the form • HTTP-Version Status-Code Reason-Phrase • The status code is a 3-digit number used by the computer. • The reason line is a friendly note for a human to read.

  35. Status code classes • 1 Informational: Request received, continuing process • 2 Success: The action was successfully received, understood, and accepted • 3 Redirection: Further action must be taken in order to complete the request • 4 Client Error: The request contains bad syntax or cannot be understood • 5 Server error: The request is valid but can not be executed by the server

  36. Error codes • 100 Continue • 101 Switching Protocols • 200 OK • 201 Created • 202 Accepted • 203 Non-Authoritative Information • 204 No Content • 205 Reset Content • 206 Partial Content

  37. Error codes II • 300 Multiple Choices • 301 Moved Permanently • 302 Found • 303 See Other • 304 Not Modified • 305 Use Proxy • 307 Temporary Redirect

  38. Error codes III • 400 Bad Request • 401 Unauthorized • 402 Payment Required • 403 Forbidden • 404 Not Found • 405 Method Not Allowed • 406 Not Acceptable • 407 Proxy Authentication Required • 408 Request Time-out

  39. Error codes IV • 409 Conflict • 410 Gone • 411 Length Required • 412 Precondition Failed • 413 Request Entity Too Large • 414 Request-URI Too Large • 415 Unsupported Media Type • 416 Requested range not satisfiable • 417 Expectation failed

  40. Error codes V • 500 Internal Server Error • 501 Not Implemented • 502 Bad Gateway • 503 Service Unavailable • 504 Gateway Time-out • 505 HTTP Version not supported

  41. Response headers • Accept-Ranges: • Age: • Etag: • Location: • Proxy-Authenticate: • Retry-After: • Server: • Vary: • WWW-Authenticate:

  42. Entity headers, common to response and request • Allow: • Content-Encoding: • Content-Language: • Content-Length: • Content-Location: • Content-MD5: • Content-Range: • Content-Type: • Expires: • Last-Modified

  43. The body • The entity-body (if any) sent with an HTTP request or response is in a format and encoding defined by the entity-header fields. • When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type and Content-Encoding

  44. example status: redirect • If you use Apache, you can create a file .htaccess (note the dot!) with a line redirect 301 old_url new_url • old_url must be a relative path from the top of your site • new_url can be any URL, even outside your site • This works on wotan by virtue of configuration set for apache for your home directory. Examples • redirect 301 /~krichel http://openlib.org/home/krichel • redirect 301 Cantcook.jpg http://www.foodtv.com

  45. The Semantic Web • The W3C has been developing a new architecture that applies knowledge representation technology to the WWW. • Using the Resource Description Framework (RDF), Statements are made using a Subject, Predicate and Object (very similar to Lisp and other predicate based languages). • Each Subject, Predicate or Object are Resources in the URI sense and are identified by URIs within an RDF Statement using XML Namespaces.

  46. The Semantic Web • The combination of Web Services and the Semantic Web should give the Web the ability to turn any existing Web Resource into a full node in a purposefully built knowledge representation system with a functional component that allows that knowledge to be acted on. • And both are based on the simple Uniform Resource Identifier.

  47. example • This statement says that the Resource identified by the URI ‘http://openlib.org/home/krichel’ was created by the person ‘Thomas Krichel’: <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <Description about="http://openlib.org/home/krichel"> <Creator xmlns="http://description.org/schema/">Thomas Krichel</Creator> </Description> </RDF>

  48. Apache • Is a free, open-source web server that is produced by the Apache Software Foundation, see http://www.apache.org • It has over 50% of the market share. • It runs best on UN*X systems but can run an a Mickeysoft OS as well. • I will cover it here because it is freely available. • Wotan runs version 2.

  49. Apache in debian • /etc/apache2/apache.conf is set main configuration file. • /etc/init.d/apache2 action, where action is one of • start • stop • restart is used to fire the daemon up or down. • The daemon runs user www-data

  50. Virtual host • On a single installation of Apache several web servers can be supported. • That means the server can behave in a different way according to how it is being addressed. • The easiest way to implement addressing a server in different was is through DNS host names.

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