1. Plattner Melanie Leschinger Bernhard
Web Technologies
Plattner Melanie
Leschinger Bernhard

2. What is this lecture about?
Introduction to the basic Web technologies
that are used to implement the „Web“ portion of Web Services:
Some historical details
Core Web Technologies
Wide area integration
Tunneling, Firewalls, EDIFACT

3. Some historical details
Start of standard groups
TCP
handles conversion between messages and streams packets IP
handles addressing of packets across networks
TCP/IP
enables packets to be sent across multiple networks using multiple standards
Telnet
One of the earliest standards for exchanging transmission, directly connect accounts on different systems.
SMTP
specifies another way of direct connection

4. Some historical details
MIME
Extension to the SMTP Protocol which supports the exchange of richer data files such as audio-, video-, and images data.
FTP
(1973) supports file transfer between Internet sites
and allows a system to publish a set of files by hosting an FTP sever
innovation  permits anonymous users to transfer files
Archie
Late 1980‘s distributed file system based on FTP
Gopher
First simple system, providing GUI

5. Core Web Technologies HTTP(HyperText Transfer Protocol)
generic, stateless protocol
governs the transfer of files across a network
developed at CERN (Central European Research Network), they also came up with the name WWW, later W3C
supports access to SMTP,FTP and other protocols
was designed to support hypertext

6. Core Web Technologies Exchanged information, can be static or dynamic
Every resource, accessible over the Web has a URL(Uniform resource locator)
HTTP mechanism is based on client/server model
typically using TCP/IP sockets

7. Core Web Technologies
since Version 1.1 HTTP requires servers to support persistent connections, to minimize overhead associated with opening and closing connections.
Typical methods on the server side are:
OPTIONS
send information about the communication options
GET
retrieve document or document produced by a program
POST
Append or attach information
PUT
Store information
DELETE
Delete the resource indicated in the request

8. Core Web Technologies Another limitation HTTP is stateless
Does not provide storing of information between requests
No indication of any relationship between two different requests
 cookies, small data structures that a web server requests the HTTP client to store on the local machine,
are used to maintain state information
e.g. cookies store recently view items on a web shop

9. REST(Representational State Transfer)
architectural style, defining the principles of distributed network systems.
is the underlying architectural model, guiding the design and development of the current and next generation web architectures

10. REST Provides a set of architectural constraints, that emphasizes
Scalability of component interaction
Generality of interfaces
Independent deployment of components
Enforce Security
Etc.

11. REST vs. Web Services
Rest promotes and recommends generic operations on resources
HTTP methods: PUT GET POST DELETE
SQL: select create drop ect.
Utilizes the caching mechanism
WS does not promote generic operations
First generation only utilizes HTTP POST
Each service defines its own application specific operations
Requires additional means of discrption,discovery mechanisms on top of the web
No caching capabilities

12. Rest Principles Web consists of addressable resources
 a user, utilizing an application selects a specific address(URL)
a specific representation of that resource is returned over the web
 places the client application into a specific state.
On accessing another URL, the client application gets another representation of the resource and in turn, transferring from the current to the new state.

13. Core Web Technologies HTML(HyperText Markup Language)
Defines a standard set of special textual indicators(markups) specifying how a Web pages words and images should be displayed by the web browser

14. Technologies for Supporting Remote Clients
Original intent of core Web Technologies  enable linking and sharing documents
It was quickly realized, that by wrapping local information systems to expose their presentation layer by using HTML documents, one could leverage the core Web technologies to have clients that are distributed across the internet.

15. B2C (Business to consumer)
Conventional 3-tier architectures are designed to operate within a single company  data exchanges occur within the safe boundaries of the company
in principle there are no reasons why the system could not be opened to other users if the need arises
ATM(automatic teller machines are an excellent example of the advantages if doing so

16. B2C
ATM(automatic teller machines are an excellent example of the advantages if doing so
client/server system
a PC with a network connection to the information services of the bank
gives customers easier access to their accounts without the bank incurring
a significant part of manual work disappears
more efficient interactions with the customer
 great service, but there are limitations

17. B2C Limitations Customers must travel to the nearest ATM,
would not be necessary,
access to their bank accounts any time,
helps extend its functionality.
This architecture is called B2C, indicating that the business allows consumers to access their information services directly

18. Problem
Users wanting to take advantage of this opportunity would need to have specialized clients for every company they want to interact with
Complexity would grow enormous -> administration

19. Solution
One of the biggest contributions of the Web  providing a universal client for such extensions
Nowadays such architectures are implemented by letting the remote computer use a Web Browser as a client
since Web Browsers are standard tools, no application specific client has to be installed

20. Web Browsers
One of the first problems  web Browsers were originally intended only to display static documents, returned by HTTP calls
Difficult to build sophisticated application specific clients for web browsers

21. Applets One answer to this problem  Applets
Java programs, can be embedded in an HTML document
When the document is downloaded, the program is executed by the JVM, presented in the browser, turning the browser into a client by sending the client code as an applet
Limitations  download the code
Advantage  complexity

22. CGI(Common Gateway Interface)
Web servers must be able to server up content from dynamic sources
How can a Web server respond to a request by invoking an application that will automatically generate a document to be returned
One of the first approaches to solve this problem, was CGI, a standard mechanism that enables HTTP servers, to interface with external applications, which can serve as „gateways“ to the local information system

23. CGI
How does CGI work
it assigns programs to URLs, so that when the URL is invoked, the program is executed
CGI programs often serve as an interface between a database and a Web server, allowing users to submit complex queries over the DB through predefined URLs
When the Web server receives request for the URL, it will run a program, that will act as a client of the database and submit the query  executing and packs the result into a HTML document  returned to remote browser

24. Servlets Performance  CGI programs involve a certain overhead
Separate process for each instance  takes time, requires a context switch in the operating system
Multiple request results – multiple process
To avoid this overhead, Jave servlets can be used instead
The idea is exactly the same as in CGI programs, but the implementation differs.

25. Servlets How do they work?
Execution and result is the same, but servlets are invoked directly by embedding servlet-specific information within an HTTP request
 run as threads of the Java server process, moreover they run as a part of the Web server
 eliminates overhead

26. Application Servers – short overview
Equivalent to middleware platforms
Main difference  intercorporation of the Web as a key access channel to the services implemented using the middleware  several important implications
The presentation layer acquires a much more relevant role
Direct consequence of how HTTP and the Web work

27. Application servers – short overview
Realized by merging the presentation layer related to the Web with the application layer of the middleware platform
Reason  to allow the efficient delivery of content trough the Web as well as to simplify the management of Web applications

28. J2EE There are two competing frameworks for Web-based middleware
Suns J2EE
Microsoft's .NET
very similar

29. J2EE
A significant aspect of application servers is the bundling of more and more functionality within the middleware platform
Providing integrated support for many different middleware abstractions
Therefore blurring the borders between application servers and other middleware

30. Application server - Application Layer
At the application layer, application servers conceptually resemble conventional middleware, provided functionality similar to CORBA, TP monitors and message brokers
Goal of application server vendors
providing a unique environment for hosting all kinds of application logic, whether Web-based or otherwise,

31. J2EE - EJB
EJB (Enterprise JavaBeans) specification is at the heart of J2EE  there the bulk of the application logic resides
An EJB is a server-side component, that delivers application-specific funktionality(responding to a request for a quote…)

32. J2EE - EJB
The EJB specification defines 3 different types of beans, based on how they interact with other components and how they manage state and persistence
Session beans
Entity beans
Message-driven beans

33. J2EE –EJB container
Provides the environment in which the beans run  all interactions go through the container
Provides a number of services
Supports transactions  freeing a developer from having to define transaction boundaries and implement the related code

34. J2EE - JNDI
Defines an interface for directory services, without mandating any implementation
Clients can bind to servers based on the object name (EJB  binding to a server involves binding to an object that provides the interface for interacting with a server)

35. J2EE - JDBC
is an API that enables developers to access almost any tabular data source by executing SQL commands from a java program
methods can be called from an EJB or directly from a servlet

36. Application Server
Offer services that simplify administration and management of the application
Caching frequently needed objects
Checking that an application is running and restarting
Object administration and security, defining user has access to which application and enforcing access restrictions

37. Application Server
Cannot match the performance of TP monitors but they try to make systems easier to develop and easier to evolve.

38. Application Server - Presentation Layer
the support for the presentation layer and for the document as the basic unit of transfer is what differentiates application servers from conventional middleware
Application servers
implement mechanisms which make the transaction between documents and arguments more efficient, flexible and manageable
provide a variety of presentation features to support the delivery of dynamically generated, personalized content to different types of clients

39. Application Server - Presentation Layer
A modern application server supports the following types of clients
Web Browsers(most common types of clients)
Applications
Such as those encountered in conventional middleware
Devices
Such as mobile phones and PDAs
programs
Web service clients

40. Wide area integration A number of strategies 3 layers Client
Middleware
Server(resource manager)
The available strategies are given by all possible combinations of these three layers

41. Wide area integration - strategies
integrating systems at the client level
at the middleware level
by connecting clients directly to the remote middleware platform,
by connecting resource managers to the remote middleware platform.
Which of these strategies is the most appropriate, depends on a number of factors

42. Middleware Extensions
The internet requires additional middleware layers between clients and servers or between servers.
 existing platforms were simply extended to allow them to interact through the internet, most middleware platforms were designed to work on a single LAN(Local area network)

43. B2B Business to Business
The number of LANs started to grow
different branches of the same company implemented their own middleware-based systems
 the need for different middleware platforms to communicate with each other, arose.
such interactions are called B2B
 fully automate the interactions

44. Firewalls and Tunneling
Acts as a barrier against unwanted network traffic
Blocks many communication channels
Can change the design space in two ways
No direct communication between the system to be integrated
Parties outside the firewall are not trusted

45. Firewalls and Tunneling
How to get through a firewall and why?
Tunneling
Tricking the firewall into believing that traffic, which otherwise should be blocked, is actually allowed
Protocols which would be blocked are hidden under protocols that are accepted by the firewall
Why  not having a direct communication channel is compounded by a necessary lack of trust on all traffic generated outside the firewall

46. EDIFACT Another important challenge
Identifying a common syntax and semantics for the data exchanged between applications
In conventional middleware platforms, this problem is hidden behind IDLs  fulfill two roles
 used to define interfaces
uses an intermediate data representation that specifies how each data type used in IDL is represented in a machine-independent manner

47. EDIFACT
In message-based systems, format and semantics of the messages or files exchanged are typically determined by the EDIFACT standard.
Provides standard templates for messages and for the contents of the message

48. EDIFACT A EDIFACT message typically contain the following fields
Interchange Header
Version of EDIFACT,IDs of sender end recipient, passwords,date,time
Message Header
Type of message
User Data segments
payload
Message Trailer
Check message completeness
Interchange Trailer
Check interchange completeness

49. EDIFACT Pros & Cons + standard structure with 3 letter codes
+ universal standard defined by EDIFACT
+ parsers can be constructed easily
- very complex standard, often unnecessarily complicated
- often only a fraction of the possible information is used
- hast to be standardized by EDIFACT before use
-requires adhoc development on the systems