Client Server Architecture - DoACT, AKT

1 Client Server ArchitectureKey concepts:- Client Server Architecture - Functional requirements in the 2-tier structures- Functional distribution in the 2-tier structures- Implementation of Business Logic at the Server - Requirements of an Open OLTP System- Benefits and Limitations of 2-tier Client / Server Architecture - The 3-tier Structures- Middleware- Component Software Model- Database Middleware- Transaction Processing and Integration Middleware- Transaction Processing Monitors- Performance Issues in TM- Two-Phase Commit Protocol in TM- Message Sensitive

2 Routing- Lifekeeper Clusters- Repositories in Client - Server Environment- 4GL Application Development Environment- Communication Models- The main standards for open transaction processingClient - Server Architecture [Salem 1992]The data processing is split into distinct parts. A part iseither requester ( Client ) or provider ( Server ). The clientsends during the data processing one or more requeststo the servers to perform specified tasks. The Server partprovide services for the basic structure is called 2-tier structureThe main basic communication modes.

3 - RPC, remote procedure call- Message-based- The Client and Server parts may reside on the same node or ondifferent nodes- A part can play the roles of a Server of a service and a Client of ananother service at the same time- A Client can be connected to several servers ClientServerFunctional requirements in the 2-tier structuresThe applications may be divided into the following logical functionalcomponents:- Presentation Servicesuser interface, dialog control- Presentation Logicuser interaction, simple validation- Business Logiccontrol flow- Distribution Servicescommunication management- Database Logicintegrity, data manipulations- Database Servicessecurity, transaction management- File Servicesfile sharing Data LogicDistributionBusiness LogicFile ServicesPresentationBusiness LogicData LogicDESKTOPC lientHOSTS erverDESKTOPC lientFunctional distribution in the 2-tier structuresFat clients .

4 Most of the functional modules of the application areperformed on the clientsFile serverLite clients : Only few functional modules of the application areperformed on the clientsRemote Data Client - Server ArchitectureClientServerPresentationBusi ness logicData logic Data servicesFile servicesRemote Presentation Client - Server ArchitectureClientServerPresentation Business logicData logicData & file servicesSplit Logic Data Client - Server ArchitectureClientServerPresentationBusi ness logicData logic Business logicData logicData & file servicesImplementation of Business Logic at the ServerActive elements in the Databases.

5 Triggers- stored proceduresTrigger:stored DBMS procedures that are executed when there is change triggering event- responseIt is stored in the DBMSC entralized management and access controlOracle SQL:CREATE TRIGGER name AFTER | BEFORE INSERT |UPDATE | DELETE ON table FOR EACH ROWBEGINPL/SQL blockENDS tored procedures:collection of SQL statements and procedural language statementsthat control the flow of the procedureIt is stored in the DBMSC entralized management and access controlIt provides faster executionMostly pre-compiledRequirements of an Open OLTP SystemTransactionsLogical unit of data processing operations- Atomicity- Consistency- Isolation- DurabilityOLTPOn-Line Transaction ProcessingCharacteristics.

6 - Short time transactions- Several concurrent transactions- Read-write transactions- Database stores the actual state of the problem domainRequirements of open OLTP systems(based on X/Open DTP model)- Vendor independence- Application portability- Distribution transparency- Modularity- Scalability- Reliability- Reconfigurability- MonitoringBenefits and Limitations of 2-tier Client / Server ArchitectureBenefits- Interoperability- Portability- Integration- Transparency- SecurityLimits- The Client and Server are tightly coupled, the Client should use theinterface protocol of the Network traffic is handled less efficiently.

7 Because it clients havea direct connection to the The network traffic increases significantly when high volumes ofdata and messages are shipped on the Asynchronous activity. - when a request is sent and an immediatereply is not required - is not The connections are limited to a single resource per The application administration is One cannot tune the response times and there is no capability toperform load balancing- The resources are scaled on the number of connected users not onthe throughput- It consumes many operating system processes and networkconnections in order to support a given set of usersThe 3-tier StructuresDistribution of the different functional modules of the

8 Applicationon three different sitesapplicationnetworkdatabase serverDBserverclientUsual distribution:1. tier: Presentation logic, lite client2. tier: Business logic, application server3. tier: Database logic, database Server - less software on the Client - increased security- more power, efficiency- higher scalability- lower support cost- complex structure- problem of heterogeneous data sourcesThe 3-tier structure can be extended to n-tier structure, containingseveral special application serversInternet-based 3-tier architectureOpen.

9 Standardized interfaceWEBnetworkdatabase serverDBserverWEB browserThe WEB servers can access the databases through CGI interfaceInterfaces among the WEB browser WEB serverHTML API<FORM .. ACTION= URL>..</FROM>2. WEB Server DBMSCLI (usually SQL)SQLEXEC(SQL-statement)2. DBMS WEB serverresult written to standard (HTML-statement)MiddlewareIn order to couple the Server and Client parts from heterogeneousenvironments in an efficient way, the basic Client serverarchitecture is extended by a new integrating resource between the clients and servers.

10 It performsthe following main activities:- translation between the different protocols- optimization of the load-balancing- security control- management of the connections ..The middleware may contain several components may reside on the Server node, on the Client nodeor on a new middleware different types of middleware- database- network- application cooperationServer ClientMiddlewareServer ClientComponent Software ModelThe clients invoke managed Server components, the namedservices. These services implement the core business structure is based on the three-tiers model: Client : it performs GUI and invokes Server componentsmiddle tier: it is composed of Server components to be invokedby the clients - control module with control data- named servicesresource manager: database managementNamed services are managed dynamically, as it offers a betteroptimization, starting and stopping the services depending on thesystem load.