The invention relates to computer networks, and specifically to a service broker for clients and servers operating in a heterogeneous computing environment.
It is increasingly common to interconnect multiple computing systems into a computer network, such as a local area network ("LAN") or wide area network ("WAN"). In a computer network, a number of computers are joined together to exchange information and share resources. A network is a distributed computing environment in which networked computers provide users with the capabilities of access to distributed resources, such as remote files and databases or printers and of distributed processing, in which an application may be processed on two or more computing systems. In such a distributed computing environment, a computing application's component functions may reside on different machines but work together. For example, each work station or personal computer ("PC") in the network often provides user interface processing and local analysis and processing, while larger, host computers may maintain a large set of files and coordinate access to large databases.
In the distributed computing environment, each application must be able to communicate and exchange information with other applications or machines in the environment. If all the machines are based on the same hardware platform, use the same operating system, and are interconnected using a single network architecture and communication protocol, connection and communication between applications and/or machines is straightforward. However, this ideal is seldom achieved. There are many different (and often mutually incompatible) computer network architectures (such as SNA, OSI, TCP/IP, DECnet, and LANs), hardware platforms (such as IBM, DEC, WANG, and Apple), operating systems (such as UNIX, OS/2, MS-DOS, VMS, and MVS), and application languages (such as COBOL, FORTRAN, PL1, C, and NATURAL). This heterogeneity presents an obstacle to the connectivity and interoperability of the systems.
FIG. 1 illustrates schematically such a heterogeneous distributed computing environment. The environment includes several "participant." Each participant may be a "client" or a "server." A participant is a "client" when it is requesting a service accessible somewhere within the computing environment. A participant is a "server" when it is providing a requested service to a client. For example, a client may be an application program, while a server may be a database, file, or program. The computing environment shown in FIG. 1 is shown for purposes of illustration as having two clients 4a and 4b and a server 6c joined together as a first LAN 5, and a two servers 6a and 6b joined together as a second LAN 7. However, each of the clients 4 and servers 6 may act as a client or a server, depending on whether it is requesting or supplying services.
The system of FIG. 1 is heterogeneous because each of the clients 4 and servers 6 may be applications running on different hardware platforms under different operating systems, and/or within different computer networks. For example, the computer for client 4a may be an IBM mid-range computer running the OS/400 operating system, the computer for client 4b may be an IBM PC running MS-DOS or OS/2, while the computer for server 6a may be a UNIX-based work station, the computer for server 6b might be a DEC mainframe computer, and the computer for server 6c might be work station running IBM's OS/2. Other computing systems might also be connected, such as a work station running Microsoft Windows or an Apple Macintosh. LAN 5 might be based on IBM's System Network Architecture ("SNA") and IBM's Logical Unit 6.2 ("LU 6.2") communications protocol, while LAN 7 might be based on a different architecture, such as OSI and its associated communications protocol. The communications protocol is a defined set of procedural rules which computers use to communicate across a network.
The use of different hardware platforms, operating systems, or network architectures and their associated communications protocols inhibits the useful exchange of information between clients and servers in a heterogeneous environment, such as that shown in FIG. 1.
Effective operation of the heterogeneous computing environment of FIG. 1, with its different and incompatible hardware, software, and network architectures, requires some mechanism for matching service requests from clients with the appropriate service offerings from servers and for managing the communications between clients and servers.
Developers of software applications that would be used in client-server relationships face three problems: software portability (platform independence); network transparency); and reliable data delivery (store-and-forward operation). These problems have not yet been adequately addressed. Simply providing a common interface, such as the Transmission Control Protocol/Internet Protocol (TCP/IP), only addresses part of the problem. Rather, the correct functionality must be provided to client-server application developers to allow applications to be developed on a "logical" platform with transparent communication across networks and with reliable data delivery.
U.S. Pat. No. 5,109,515 to Laggis ("Laggis") discloses an apparatus for interconnecting DOS-based PCs, UNIX-based intermediate computers (acting as servers), and a mainframe computer, to provide the PCs services available on the servers and/or mainframe. Each PC is connected to a server via a patch. Patch 21 traps calls by PC applications to services on a server or mainframe. The trapped requests are directed to driver 31 on the associated server. Driver 31 collects the trapped requests from PCs and directs these to user level request server 32 on the server. Request server 32 performs file and resource serving and locking services to make requested resources available to the PC's operating system. Request server 32 calls on NETSVR process 33 to find resources on other servers and on APISVR to get the services on the mainframe. The request server 32 returns notes to patch 21, which forwards trapped user requests to PC's operating system to service the request. The PC's operating system views the server as a peripheral. Laggis is concerned only with file transfer between a PC (running PC-DOS) and a mainframe via a UNIX system.
U.S. Pat. No. 4,604,686 to Reiter, et al. ("Reiter") discloses an interface for inteconnecting user terminals 12 and diverse processors running different types of databases 14. The interface is a file-driven computer program for controlling access to the many databases by the user terminals. The interface is loaded with files having information relating to interfaces used with different processors, query languages, and data base managers, and information on the location of each kind of on formation and method of retrieval. A user at one of the user terminals makes a request for specific information to the interface. The interface in turn couples to each required data base (mimicking an asynchronous terminal), retrieving the data. Reiter provides remote access to heterogeneous computer systems in the form of asynchronous terminal emulation. Reiter controls data retrieval from these systems by a user-written command procedure, and presents the data in specific formats on the user terminal, again controlled by user-written command procedures. provides data retrieval from these systems. Reiter thus describes a very specific means to automate dial-up, logon, data access, and screen formatting procedures.
There is thus a need for a system that facilitates cooperative processing among application programs in a heterogeneous computing environment and that provides store-and-forward messaging, conversational program-to-program communication and remote procedure calls. Such a system should support communication between applications independent of operating system, hardware, network/communication protocol, and programming language.