1. 1 Engineering Web Based Legacy Systems By Kanchana Eramudugoda Distributed Computing – CS843

2. 2 Content  What is a Legacy System?  Typical Problems Associated with it  Standards for Service Web  Migrating to Web-based  Migrating Components in to Network Environment

3. 3 What is a Legacy System? "A computer system or application program which continues to be used because of the prohibitive cost of replacing or redesigning it and despite its poor competitiveness and compatibility with modern equivalents." Examples : IBM AS/400 IBM Mainframe Tandem

4. 4 They are very difficult and may not easy to expand It typically runs on absolute hardware, which is expensive and hard to maintain Maintaining the software is expensive; Due to lack of documentation and lack of understanding of the internal working of the system, tracing can be costly and time consuming Problems Associated with Legacy Systems

5. 5 Simple Object Access Protocol - SOAP is an XML based messaging protocol. It usually used for exchanging information and Remote Procedure Call over HTTP(not necessary) SOAP consists of 4 parts 1. SOAP Envelope – defines the content of the message 2. SOAP Encoding rules – defines the serialization mechanism 3. SOAP RPC Representation – How to make calls and responses 4. Protocol Binding – HTTP, SMTP Standards For Service Web (SOAP, WSDL,UDDI)

6. 6 Few Things to Consider When Writing a SOAP M essage MUST be encoded using XML Message MUST use the SOAP Envelope namespace Message MUST use the SOAP Encoding namespace Message must NOT contain a Document Type Definition (DTD) reference Message must NOT contain XML Processing Instructions Some sample Skeleton of SOAP <soap:Envelope xmlns:soap="http://www.w3.org/2001 /12/soap-envelope" soap:encodingStyle="http://www.w3.o rg/2001/12/soap-encoding">.........

7. 7 Web Services Description Language - WSDL is a XML language for describing web services as a set of endpoints (ports) of message exchange. Each endpoint consists of, Definitions of operations, messages, binding protocol and message format. WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes. A WSDL service definition applies several layers of abstraction. There are six layers: 1. Data types that the service operates on 2. Message types the service can receive/send 3. How these messages combine into operations 4. What protocols the service will bind to 5. WSDL ports (operation + protocol) 6. A service on a given port

8. 8 Main Structure of the WSDL Document ….. definition of types........ ( The data types used by the web service ) …. definition of a message.… ( The messages used by the web service ) …. definition of a port...... ( The operations performed by the web service – just like a module or class ) ….. definition of a binding.... ( The communication protocols used by the web service ) message name="getTermRequest"> Sample Code

9. 9 Universal Description, Discovery, and Integration - UDDI is the building block that businesses can use to quickly, easily, and dynamically find and transact with each another, using their preferred applications. UDDI functions include: Service Provider Provides and publishes e-business web services Service Registry SOAP-activated web service yellow pages Service Requester Finds required services and binds client to those services

10. 10 Migrating Components in to Network Environment Representation of data/interface using XML XML Representation of Component Interface CORBA IDL module AVL{ iinterface corba_SampleRec; typedef char corba_ubi_trBool; interface corba_SampleRec{ void putName(in string val); string getName(); void putNode(in corba_ubi_btNode val); corba_ubi_btNode getNode(); long getDataCount(); void putDataCount(in long aval); }; <Component name=”AVL” href=http://www.swen.uwaterloo.ca/BookStock>http://www.swen.uwaterloo.ca/BookStock <OpName name=”getNameString” srcMethod=”getName”/>

11. 11 Wrapping CORBA objects with SOAP Enabling of access to CORBA objects with out installing the ORB runtime capability on the clients side, thin client s or lightweight clients, is much harder. Therefore to make it easy SOAP protocol is used as a messenger between CORBA objects and the web services. Web Clients Web Server Application Server Servlet Engine SOAP runtime SOAP/CORBA IDL Translator CORBA Server CORBA Components HTTP/SOAP HTTP GET/POST Process the HTTP/GET or POST requests Interpretation and Dispatching of messages It is a Collection of Java Beans; Encapsulate all the services including serialization and de- serialization

12. 12 SOAP interface XML with the corresponding CORBA IDL definitions. struct EchoData { long aLong; boolean aBool; string aString; }; EchoData getData( in long l, in boolean b, in string s)

13. 13 Conclusion It is beneficial to engineering web based legacy system. Because Allows the company to take advantage of the latest technologies available Web-based applications and services promise more flexible, efficient and cost-effective operations than the legacy systems that are showing signs of age and years of patching and fixing.

14. 14 Questions ?