co-funded by the european union semantic cms community designing semantic cms – part ii copyright...

Co-funded by the European Union

Semantic CMS Community

Designing Semantic CMS – Part II

Copyright IKS Consortium1

LecturerOrganization

Date of presentation

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Introduction of Content Management

Foundations of Semantic Web Technologies

Storing and Accessing Semantic Data

Knowledge Interaction and Presentation

Knowledge Representation and Reasoning

Semantic Lifting

Designing Interactive Ubiquitous IS

Requirements Engineering for Semantic CMS

Designing Semantic CMS

Semantifying your CMS

Part I: Foundations

Part II: Semantic Content Management

Part III: Methodologies

(2) (1)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

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What is this Lecture about?

We have seen ... ... how requirements for

semantic content management are defined in a systematic way.

... a list of industry needs.

What is missing? An efficient way to design an

architecture for a semantic CMS that meets the defined requirements

Copyright IKS Consortium

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Designing Interactive Ubiquitous IS

Requirements Engineering for Semantic CMS

Designing Semantic CMS

Semantifying your CMS

Part III: Methodologies

(7)

(8)

(9)

(10)

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How to design a semantic CMS?


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Conceptual Reference

Architecture

Technical Architectural

Style

Part 1IKS Reference

Architecture

Part 2REST Architecture

What does the architecture of a

semantic CMS look like?

How can a semantic CMS be realized?

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REST Architecture

Stateless server are easy to replicate – scalable architecture Caches are only possible in stateless communication


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ClientsOriginServer

http

Gateway, Load

Balancer

C

+ Cache

C

C

Proxy

http

http

C

http

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RESTful Interfaces

REST is based on uniform interfaces between the components of the architecture.

A RESTful interface has to fulfill the following constraints: Identification of resources Manipulation of resources through representations Self-descriptive messages Hypermedia as the engine of application state


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Roy Thomas Fielding, Architectural Styles and the Design of Network-based Software Architectures, PhD Thesis, http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm, 2000

http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm

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REST Applied to Web Technologies

Resource identification by applying REST toUniversal Resource Identifiers (URIs) http://upb.de

Self-descriptive messages and resource representation by using HTML, XML and JSON

Resource manipulation through representations by applying REST to HTTP HTTP POST to http://upb.de/news to create a new posting

Code-on-demand by using JavaScript Include JavaScript in HTML


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http://upb.de/

http://upb.de/news

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Resource Oriented Architecture (ROA)

One fundamental concept of REST are resources Design web applications by focusing on resources and

applying ROA design principles A web service is a resource Each entity that is part of the web application is a resource

ROA applied to URI Each resource has a stable URI Map hierarchies of resources by using sub paths in URIs Use URI parameters to specify additional constraints on

the resource, for example:

/path/to/resource?param1=value1&param2=value2 Copyright IKS Consortium

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ROA applied to URI Bank

http://www.bank.de/ All clients of the bank

http://www.bank.de/clients Single client identified by client number

http://www.bank.de/clients/815 All accounts of client 815

http://www.bank.de/clients/815/accounts Single account number 4538734 of client 815

http://www.bank.de/clients/0815/accounts/4538734 Balance of account 4538734 of client 815

http://www.bank.de/clients/815/accounts/4538734/balance


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Bank

Client

Account

Balance

*

*

1

clients

accounts

balance

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REST applied to HTTP Meta-data are stored in the header as

name-value pairs, for example Language information Data format Cache control User name, security token

Payload is transported in the HTTP

body, for example a SOAP message when using standard

web services a JSON string in case of lightweight

web servicesCopyright IKS Consortium

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HTTP Message

HTTP Header

Name = ValueName = Value

HTTP Body

0101010101010

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Representation of Resources Each resource has its URI By accessing the URI the resource can be retrieved in

different representations (formats) HTTP uses content negotiation with the accept-*

header for this, for example


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GET /clients/0815Host: bank.deAccept: text/htmlAccept-Language: de, en

Returns a HTML representation of the client 0815. Preferred languages are first German then English.

GET /clients/0815Host: bank.deAccept: application/jsonAccept-Language: en, de

Returns a JSON representation of the client 0815. Preferred languages are first English then German.

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HTTP Content Negotiation A HTTP Request supports four Accept-* fields

Accept: List of accepted media types Accept-Charset: List of accepted character sets and

character encodings, respectively. Accept-Encoding: List of accepted encodings of the

content. Accept-Language: List of accepted languages.

The values are comma separated lists of weighted properties, for example Accept-Language: de, en;q=0.5, fr;q=0.2 Client accepts German, English, and French with

German weighted as 1, English 0.5, and French 0.2


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For further reading have a look at the Internet Engineering Task Force (IETF)“httpbis” working group page: http://datatracker.ietf.org/wg/httpbis/

http://datatracker.ietf.org/wg/httpbis/

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HTTP Media Types

text/* for text data, e.g. html image/* for image data, e.g. gif video/* for video files, e.g. mpeg audio/* for audio files, e.g. mp3 application/* for not interpreted binary data, e.g. xml, json

application/vnd.* for vendor specific formats, e.g. ms-excel

application/x-* for non-standard files, e.g. latex application/x-pkcs* for (public key) cryptographic files

multipart/* for data in multiple parts, e.g. form-data message/* for messages, e.g. e-mail format rfc-822 model/* for data with multidimensional structure, e.g. vrml


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Manipulation of Resources via HTTP

Use HTTP methods to access and manipulate resources.

Standard web services only use HTTP POST and GET to send SOAP messages, but there is more OPTIONS – to request information about the communication

options available to a given URI HEAD – is identical to GET but the server must not return a

message-body in the response PUT – to store the enclosed resource under the request URI DELETE – to delete the resource identified by the request URI TRACE – to see what is being received at the other end of the

request chain and use that e.g. for testing


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Example REST Call

Request

Response


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POST http://www.bank.de/clients/815/accounts/4538734/balance

HTTP-Header:Accept: application/json

HTTP-Body: { “amount” : -100}

HTTP-Header:Content-type: application/json

HTTP-Body: { “balance” : -500}

Resource identified by URIHTTP Operation

Parameter

Return value

Format

Format

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Idempotent HTTP Methods

Idempotence:The side-effects of N > 0 identical requests is the same as for a single request.

Idempotent HTTP methods are GET, HEAD, PUT, DELETE

Methods that must not have any side effects, and so are inherently idempotent OPTIONS and TRACE

Note, a sequence of requests may not be idempotent even if all used methods in that sequence are idempotent


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Source: RFC-2616 http://www.w3.org/Protocols/rfc2616/rfc2616.html

http://www.w3.org/Protocols/rfc2616/rfc2616.html

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REST from the Command Line

cURL tool available for all major platforms On Windows you may need Microsoft Visual C++ 2010

Redistributable Package cURL is a command line tool for transferring data with

URL syntax Examples:

GET a resource

GET resource as XML

POST to a resource


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curl http://host.de/path/to/resource

curl –H "Accept: application/xml" http://host.de/resource

curl -d "name=Smith" http://host.de/resource

Download at http://curl.haxx.se/

http://curl.haxx.se/

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HTTP OPTIONS

Reponses are not cacheable Example: Check OPTIONS of http://apache.org


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curl –i –X OPTIONS http://apache.org

HTTP/1.1 200 OKDate: Thu, 10 Nov 2011 12:50:12 GMTServer: Apache/2.3.15-dev (Unix)Allow: GET,HEAD,POST,OPTIONS,TRACECache-Control: max-age=3600Expires: Thu, 10 Nov 2011 13:50:12 GMTContent-Length: 0Content-Type: text/html; charset=utf-8

Supported HTTP methods

no side-effects



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HTTP GET

Retrieve whatever information (in the form of an entity) is identified by the request URI.

If the URI refers to a data-producing process (service), the returned information is the produced data (not the service).

Cacheable Possibility of conditional GET by header

If-Modified-Since, If-Unmodified-Since, If-Match, …

Example: Get website if modified since November 10, 2011 - 2:30 pm


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idempotent

curl -i -H "If-Modified-Since: Thu, 10 Nov 2011 14:30:00 GMT" \http://apache.orgHTTP/1.1 304 Not Modified



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HTTP HEAD

The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response.

Often used for testing hypertext links for validity, accessibility, and recent modification.


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idempotent

curl -i –X HEAD http://www.uni-paderborn.de

HTTP/1.1 200 OKServer: ApacheSet-Cookie: fe_typo_user=cdb2bbfa6be0c06c41c2d050d2492bb4;curl -i –X HEAD http://google.de

HTTP/1.1 301 Moved PermanentlyLocation: http://www.google.de/Expires: Sat, 10 Dec 2011 15:07:42 GMTCache-Control: public, max-age=2592000Server: gws



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HTTP PUT

Use PUT to create a resource at a given URI The PUT method requests that the enclosed entity be

stored under the supplied Request-URI. Different meaning of URI in POST and PUT

POST: URI identifies resource to handle the request PUT: URI identifies entity enclosed with the request

Return codes: New resource created (201 Created) Existing resource modified (200 OK or 204 No Content) Request applied to different URI than specified by the

Request-URI (301 Moved Permanently)Copyright IKS Consortium

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idempotent



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HTTP POST

Accept an entity as a new subordinate of the resource identified by the URI. Use 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.

Example to post a message with topic “Test” and text “Hello World”:


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curl -d "topic=Test&text=Hello%20World" \http://some.host.com/messages

URL encoded string



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HTTP DELETE

The DELETE method requests that the origin server delete the resource identified by the Request-URI.

Deletion can mean to move the resource to inaccessible location.

Responses are not cacheable. Return codes Delete successful (200 OK) Delete accepted but not enacted yet (202 Accepted) Delete enacted but no entity in response (204 No Content)


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idempotent

curl -i –X DELETE http://google.de

HTTP/1.1 405 Method Not AllowedServer: GFE/2.0


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HTTP TRACE

The TRACE method is used to invoke a remote, application-layer loop-back of the request message.

A TRACE request MUST NOT include an entity. The final recipient is either the origin server or the first

proxy or gateway TRACE allows the client to see what is being received

at the other end of the request chain and use that data for testing or diagnostic information.

For security reasons most web servers don’t allow this.


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no side-effects



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Mismatches between REST and HTTP

Cookies Back-button confusion if application state is stored in cookie. Allow data to be passed without sufficiently identifying its

semantics. Becoming a concern for both security and privacy. Possibility to track users as they browse between sites.

Mandatory Extensions HTTP header field names can be extended at will, but only when

the information they contain is not required for proper understanding of the message.

By extending the header with mandatory fields that need to be interpreted to understand the message – the REST concept is broken.


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WADL – Web Application Description Language GET http://www.bank.de/application.wadl

Describing REST Interfaces


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Source and further reading: http://www.w3.org/Submission/wadl/

<?xml version="1.0" encoding="UTF-8"?><application xmlns="http://wadl.dev.java.net/2009/02"> <resources base="http://www.bank.de/"> <resource path="/clients/{cid}"> <param name="cid" style="template" type="xsd:int" /> <method name="GET"> <response> <representation mediaType="application/xml"/> <representation mediaType="application/json"/> </response> </method> </resource> </resources></application>

Resource

Operation

Supported response formats

Parameter type

Parameter

http://www.w3.org/Submission/wadl/

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REST API Example: Twitter

Twitter REST API for getting followers GET followers/ids Returns an array of numeric IDs for every user following

the specified user. Resource URL

Parameters: user_id, screen_name, cursor, stringify_ids


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Source and further reading: https://dev.twitter.com/docs/api

http://api.twitter.com/1/followers/ids.format

Server Resource Format

Format: Should useHTTP contentnegotiation instead.

https://dev.twitter.com/docs/api

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REST API Example: Twitter II

Request:GET http://api.twitter.com/1/followers/ids.json?screen_name=fctwitt

Response:{ "previous_cursor": 0, "ids": [ 143206502, 143201767, 777925 ], "previous_cursor_str": "0", "next_cursor": 0, "next_cursor_str": "0"}


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Note:The service needs authentication that is not part of this example. For more information see Twitter API doc and the OAuth protocol.

To get information about user 143206502 use:

GET/users/lookup.json?user_id=143206502

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Hands-On RESTful Services in Java

Java API defined by JSR 311 calledJAX-RS: The Java API for RESTful Web Services Stable version 1.0 Version 2.0 in progress (started Jan 2011)

Implementations Jersey - http://jersey.java.net/ Apache Wink - http://incubator.apache.org/wink/ JBoss Resteasy - http://www.jboss.org/resteasy

Download example Jersey demo webapp from http://jersey.java.net/nonav/documentation/latest/getting-st

arted.html


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JAX-RS Source: http://jcp.org/en/jsr/summary?id=311

http://jersey.java.net/

http://incubator.apache.org/wink/

http://www.jboss.org/resteasy

http://jersey.java.net/nonav/documentation/latest/getting-started.html

http://jersey.java.net/nonav/documentation/latest/getting-started.html

http://jcp.org/en/jsr/summary?id=311

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Jersey JAX-RS Preparations

Download and install Eclipse http://www.eclipse.org

Download and install Apache Maven http://maven.apache.org/

Download hello world web app https://maven.java.net/service/local/artifact/maven/redirect?r=releases&g=com.sun.jersey.samples&a=hello

world-webapp&v=1.10&c=project&e=zip

Unzip web app. In web app directory do: Create Eclipse project by executing

Compile and run webb app by


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$ mvn clean package jetty:run

$ mvn eclipse:eclipse

http://www.eclipse.org/

http://maven.apache.org/

https://maven.java.net/service/local/artifact/maven/redirect?r=releases&g=com.sun.jersey.samples&a=helloworld-webapp&v=1.10&c=project&e=zip

https://maven.java.net/service/local/artifact/maven/redirect?r=releases&g=com.sun.jersey.samples&a=helloworld-webapp&v=1.10&c=project&e=zip

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Jersey JAX-RS: Step 1

Create a class that extends Application


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@ApplicationPath("/")public class MyApplication extends Application { @Override public Set<Class<?>> getClasses() { final Set<Class<?>> classes = new HashSet<Class<?>>(); classes.add(HelloWorldResource.class);

return classes; }}

javax.ws.rs.core.Application

Must return the resource classes of the application.

Create a set of resource classes.

Add resource class.

Return resource classes.

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Create HelloWorldResource class


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@Path("/helloworld")public class HelloWorldResource {

@GET @Produces("text/plain") public String getHelloWorldMessage() {

return "Hello World"; }}

Class is a Plain-Old-Java-Object (POJO)

HTTP method. Could also be @POST, @DELETE, etc.

Format (media type) of data sent in response.

Any method name.

Return the plain text as a String.

Request URI path of this resource.

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Test HelloWorld RESTful Service


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curl -i http://localhost:8080/helloworld-webapp/helloworld

Host:Port Webapp name Resource path

HTTP/1.1 200 OKContent-Type: text/plainTransfer-Encoding: chunkedServer: Jetty(6.1.24)

Hello World The content.

The content format.

HTTP response code.

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Jersey JAX-RS: Another response code

Change the response code from 200 OK to 500 Internal Server Error


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@GET @Produces("text/plain") public Response getHelloWorldMessage() { // Some error return Response.status(Status.INTERNAL_SERVER_ERROR) .entity("Ups.") .build(); }}

javax.ws.rs.core.Response

Set response code.

Set entity (content) sent with the response.

HTTP/1.1 500 Internal Server ErrorContent-Type: text/plain

Ups.

Service response.

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Jersey JAX-RS: Return HTML

Return HTML instead of plain text.


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@GET @Produces(MediaType.TEXT_HTML) public Response getHelloWorldMessage() { StringBuilder html = new StringBuilder(); html.append("<html><body>"); html.append("<h1>Hello World!</h1>"); html.append("</body></html>");

return Response.ok(html.toString()).build(); }}

Produces “text/html”

Create HTML document.

Return OK with HTML as content.

Note: Instead of generating HTML code like this, modern

web frameworks use a template engine.

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Jersey JAX-RS: Test HTML Service

via cURL

via Web Browser


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HTTP/1.1 200 OKContent-Type: text/html

<html><body><h1>Hello World!</h1></body></html>

curl –i http://localhost:8080/helloworld-webapp/helloworld

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Jersey JAX-RS: Use Path Parameters

Return HTML instead of plain text.


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@Path("/hello/{msg}")public class HelloWorldResource {

@GET @Produces(MediaType.TEXT_HTML) public Response getHelloMessage(@PathParam("msg") String msg) { StringBuilder html = new StringBuilder(); html.append("<html><body>"); html.append("<h1>Hello ").append(msg).append("</h1>"); html.append("</body></html>");

return Response.ok(html.toString()).build(); }}

Path parameter ‘msg’.

Insert message.

Return OK with HTML as content.

‘msg’ is mapped from the URI @Path placeholder.

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Jersey JAX-RS: Test Path Parameter

http://localhost:8080/helloworld-webapp/hello/Uni

http://localhost:8080/helloworld-webapp/hello/Paderborn


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http://localhost:8080/helloworld-webapp/hello/Uni



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Jersey JAX-RS: Return JSON Object

Return data about a person in JSON format.


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@Path("/person/{name}")public class PersonResource {

@GET @Produces(MediaType.APPLICATION_JSON) public Response getPerson(String name) throws JSONException { JSONObject jo = new JSONObject(); jo.put("name", name); jo.put("age", 44); jo.put("height", 1.85); return Response.ok(jo).build(); }}

Produces “application/json”

Resource URI is now a person’s name.

Create and return the JSON object.

HTTP/1.1 200 OK

{"name":"john","age":44,"height":1.85}

Response withname = john

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Client

RESTful Service and Client Clients retrieve data via

HTTP requests to RESTful services.

Clients are web enabled devices like web browsers, smartphones, tablets, …

Requests are often performed in the background.

Often JavaScript is used at client-side.


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Server

RESTful Service

HTTPRequest

HTML,XML,JSON

User Interface

JavaScript

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What is JavaScript?

Official name is ECMAScriptaccording to the ECMA-262 standard.

JavaScript refers to the language implementation of ECMA-262 by Netscape and the Mozilla Foundation.

It was designed to add interactivity to HTML pages. JavaScript is a loosely typed scripting language (a scripting

language is a lightweight programming language). JavaScript is an interpreted language (means that scripts are

directly executed without compilation). Client-side JavaScript is usually embedded directly into HTML

pages and interpreted by the browser.

Further reading: http://www.ecma-international.org/publications/standards/

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http://www.ecma-international.org/publications/standards/Ecma-262.htm

http://www.ecma-international.org/publications/standards/Ecma-262.htm

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JavaScript is NOT…

JavaScript is not Java!Java and JavaScript are two completely different languages in both concept and design!

JavaScript is not simple!“JavaScript is a full-featured programming language, as complex as any and more complex than some.Using JavaScript for nontrivial tasks may be frustrating without a solid understanding of the language.”

JavaScript is not object-oriented!JavaScript is an object-based language, i.e. it does not support capabilities of classification, inheritance, encapsulation and information hiding.


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Source: David Flanagan,JavaScript – The Definitive Guide. O’Reilly, 2006

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JavaScript for typical tasks JavaScript gives web engineers a programming tool to

create interactive web sites. JavaScript can react to user events

<div onclick="doSomething();">…</div> JavaScript has access to the browser via client objects,

e.g. document: content of current HTML document navigator: information about used web browser

JavaScript can add dynamic content to an HTML page:


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var h1Element = document.createElement("h1");var headText = document.createTextNode("Hello");h1Element.appendChild(headText);Document.appendChild(h1Element);

Create Elements

Append Elements

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JavaScript Short Overview

Compute table of factorials:


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<body> <h2>Table of Factorials</h2>

<script type="text/javascript">

var fact=1; for (i=1; i < 10; i++) { fact = fact*i;

document.write(i + "! = " + fact + "<br>"); } </script></body>

Embedded JavaScript in HTML page

New variable: No static type declaration!

Start loop from 1 to 10

Compute and assign next value

Dynamically write content to HTML page.

HTML code

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JavaScript and jQuery

jQuery is a fast and concise JavaScript Library for HTML document traversing, event handling, animating, and interactions.

Add jQuery to the page:


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Source and further reading: http://jquery.com/

<html> <head> <title>Demo</title> <script src="jquery.js" type="text/javascript"></script> </head> <body> … </body></html>

jQuery is defined and included here as a separate JavaScript file.

http://jquery.org/

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Call RESTful Web Service with jQuery


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<script type="text/javascript"> function getData() { jQuery.ajax({

type: "GET", url: "http://localhost:8080/helloworld-webapp/person/jim", dataType: "json",

success: function(data, textStatus, jqXHR) { alert(data.name + " is + " data.age + " years old."); },

error: function(jqXHR, textStatus, errorThrown) { alert("Ups."); } }); }</script>

Perform HTTP REST call usingjQuery’s ajax() operation.

Specify type, resource URI, and format of REST service.

On success show person’s data received in JSON format.

On error show a message.

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REST for Interactive Web Applications

RESTful services are a key technology for dynamic and interactive web applications.


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Click

Message box with data retrieved from the server. No page reload!

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REST and AJAX Asynchronous

JavaScriptAnd XML (or JSON, …)

AJAX engine processes HTTP requests asynchronously to the user interface.

RESTful services on the server

AJAX is not bound to XML – may also beJSON, HTML, Text, …


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Client Browser

User Interface

JavaScript AJAX Engine

JavaScriptCall HTML, CSS

HTTPRequest

HTML,XML,JSON

Server

RESTful Service

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Lessons Learned ...

Now you should know ... ... the architectural requirements for a semantic CMS. ... the integration concept of two loosely coupled columns. ... the components of the reference architecture ... how the reference architecture model can used to build

a semantic CMS from scratch and how an extended system can be extended


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co-funded by the european union semantic cms community designing semantic cms – part ii copyright...

Documents

http http post

http message http header

http request

client number http

uri bank http

http content negotiation

semantic cms semantifying

html copyright iks consortium