2-Tier Vs 3-Tier
- Instead of Fat clients and fat servers these terms can be used.
- It is all about how you split the client/server applications into functional units.
- These functional units can be assigned to either the client or to one or more servers.
- The most typical functional units are:
- User Interface
- Business Logic and
- the Shared Data
- In 2-tier, the application logic is either buried inside the User Interface on the client or within the database on the server (or both)
- 2-tier system examples: File Servers and Database Servers with stored procedure.
- In 3-tier, the application logic (or) process lives in the middle-tier, it is separated from the data and the user interface.
- 3-tier systems are more scalable, robust and flexible. In addition, they can integrate data from multiple sources.
- Examples: TP Monitors, Distributed Objects and the Web.
Different Meanings for 3-tier:
First:
tier 1 – Application in PC
tier 2 – Departmental Servers
tier 3 – Enterprise Servers
Then:
tier 1 – Partitions across client
tier 2 – local database
tier 3 – enterprise database
Now:
tier 1 – Client
tier 2 – Application Server
tier 3 – Database Server
What is Middleware?
- Middleware does not include the software that provides the actual service that’s in the server’s domain.
- It also does not include the user interface or the application’s logic that’s in the client’s domain.
- It starts with the API set on the client side that is used to invoke a service, and it covers the transmission of the request over the network and the resulting response.
- Middleware divided into two broad classes:
(a) General Middleware (b) Service-Specific Middleware
(a) General Middleware
- It is the substrate for most client/server interactions
- It includes the communication stacks, distributed directories, authentication stacks, distributed directories, authentication services, network time, remote procedure calls, and queuing services.
- Products that fall into the general middleware category include DCE, ONC+, NetWare, NamedPipes, LAN Server, LAN Manager, Vines, TCP/IP, APPC and NetBIOS.
- Message Oriented Middleware (MOM) products from Peerlogic, Covia, Message Express, System Strategies and IBM.
- These are depends on message queue system and increases portability, interoperability, flexibility.
(b) Service-Specific Middleware
- It is need to accomplish a particular client/server type of service.
- This includes
- Database-specific middleware such as ODBC, DRDA, EDA/SQL, SAG/CLI and Oracle Glue.
- OLTP-specific middleware such as Tuxedo’s ATMI and /WS, Encina’s Transactional RPC, and X/Open’s TxRPC and XATMI
- Groupware-specific middleware such as MAPI, VIM, VIC, SMTP and Lotus Notes Calls
- Object-specific middleware such as OMG’s CORBA and Microsoft’s Network OLE (or DCOM)
- Internet-specific middleware such as HTTP, S-HTTP and SSL
- System Management-specific middleware such as SNMP, CMIP and ORBs.
