Microcomputers have an important role to play as distributed databases on a local area network, where each of the system functions is specialized on different microcomputers

Abstract: The role of a DDBMS is to provide overall system integrity, appropriate data access, and recovery over the whole network. Many of the supermicros with pow~ul16 and 32 bit architectures will soon be running advanced DBMS and DDBMS sofiware, thus, playing an important role as a dism’buted database on a network. The article discusses this and future trends.

Kqwords: data processing, microcomputers, dism’buted databases, computer networks.

Microcomputers and distributed database management systems by FRANK POOLE

C ompanies with multisite opera- tions often have very similar information requirements on

different sites. Typical of this situa- tion might be a distribution company with several warehouses, where iden- tical computer systems are installed in the warehouses to control operational dataflows. These computers may in turn be linked to a central machine which draws on the operational data to perform management control tasks. This constitutes a hierarchical net- work, and company procedures may well indicate that optimal cost/benefit is obtained from using a microcom-

puter at each of the warehouses. Alternatively, if we consider the

problem of a steel stockholder with several sites, where the salesmen at each site are allowed to draw steel stock from any site in order to satisfy a customer order, then one solution to this problem may involve a computer at each site without any machine being a natural master. Thus, the system may be implemented as a network where the nodal computers are of equal status, and able to inter- communicate at will. In fact, the geographical position of the sites may force two sites to communicate via

Frank Poole is principal lecturer at Sheffield City Polytechnic.

A distribution company might have several warehouses with identical computer ~stems fm dataflow, controlled centrally by a machine for management tasks.

20 0011-684X/84/060020-02$03.00 0 1984 Butterwortb & Co (Publishers) Ltd. data processing

systems

intermediary sites, but this is an issue of network software functionality and cost, rather than one of a master-slave relationship between the nodal com- puters.

With the advent of super-micros with powerful 16 bit and 32 bit architectures, many of the network architectures, hitherto the domain of minicomputers, are susceptible to the microcomputer. It seems reason- able to assume that these supermicros will soon be running advanced DBMS software. Moreover, with the recent publication of proposals for the Codasyl-based distributed DBMS (DDBMS), it seems reasonable to assume that implementation of these ideas will take place on supermicros as well as on minis and mainframes.

Distributed database management systems

The DDBMS philosophy implies that there is control software, which itself may be distributed over several machines, that has knowledge of the data placement strategy and file struc- tures, and is invoked when access to the data is required. Such software will include additional features such as privacy control, concurrency con- trols, consistency checking and re- covery mechanisms. These issues are much more complex for distributed databases than for a single-site data- base. This raises the natural question as to why anyone should bother to implement such complex systems. The answer is at least two-fold. First, the aim of a DDBMS is to provide overall system integrity, appropriate data access and recovery over the entire computer network. It is vital that future implementations attain this objective without relinquishing the equally important objective of user friendliness. The second point relating to the need for such a system arises from a potential scenario of the future of data processing. If problem solution semantics can be defined at

the outset, then the complexity of the applications programming task can be reduced significantly.

It is this combination of the data- logical and process-based views that is giving impetus to fourth generation software, where increases of lo-fold are claimed for programming effici- ency. Short-term solutions, such as simple program generators, will un- doubtably be replaced by systems which allow the user to develop a view of the database. This will also include functional activities, thus, defining the screens, reports and process units to build on the data structure view and providing run-time executable code. This shift in emphasis to tackle the problem of the labour-intensive programming task, and to provide robust reliable applications code is a natural development of the database philosophy.

Microcomputers in DDBMS

From the proceeding discussion we see that microcomputers may have a valid role to play in the future deve- lopments of distributed database management systems and their exten- sions on wide area networks (WAN). However, there are another two classes of system where microcom- puters might well be used as a form of distributed database. The first of these is the local area network. Many examples exist of microcomputers linked by networking software to shared resources such as printers and discs. Typical of this type of system is a series of IBM PCs running under PCNET. In this type of system, the data may be distributed across several disc units, some of which may be local to an individual workstation. This forms a microcosm of the WAN approach in that similar problems of data distribution and user access pro- files arise. However, extending the capability of each workstation to cope with the full extent of the software required would be prohibitive at this time. One approach to this problem is

to specialize the system functions. Thus, a network database processor might be introduced to replace the file server. This degree of specialism might be extended to include such database functions as privacy, con- currency control, recovery and consis- tency. This type of specialism has, in fact, been implemented on specific projects such as the DEMOS system developed at the National Physical Laboratory. Currently, at least one database product is being developed around the concept of a backend database machine. This should reduce the load on the main processor unit and speed up access times in much the same way as a front-end machine relieves the main processor unit of the tedium of handling remote devices.

Whatever approach is adopted architecturally - however data, hard- ware and the DDBMS software itself are distributed - it is of paramount importance that the architecture is transparent to the user. Of course, the database administrator will be con- cerned with the distribution strategy in order to tune the system. One might be tempted to conclude that the microcomputer has come of age and that the old restrictions imposed by 8 bit microprocessors are a past phase in the evolutionary development of the new technology. Certainly, increased power and greater flexibility have opened up an avenue for distributed database software development on microcomputers. Such thoughts are attractive as long as it is borne in mind that the trend in the area of fifth generation systems is to move away from increasingly sophisticated general purpose microprocessors, to simpler specialized processors which when coupled together provide a more elegant internal architecture with a high degree of parallelism. Such architectures may well have implications for code construction, so obviously the end is not yet in sight.

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Sheffield City Polytechnic, Pond Street, Shef- field Sl IWB, UK. Tel: (0742) 20911.

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