Web-Based Process Control Systems: Architectural Patterns, Data Models, and Services
چکیده
In our paper we discuss results of the real-life project in the domain of Information Handling Systems for Technological Process Control (TPC-IHS) development in the gas-transport and gas-production branches in the Ukraine. We emphasize important requirements, which have to be satisfied by analyzing and designing of Web-based TPC-IHS. Architectural design patterns, which were elaborated with respect to real-time operating mode issues, and multi-level distributed topology of TPC-IHS are presented using UML-notation. We introduce the Integrated Node Database model, which includes the processoriented storage structures and appropriate functionality. Advanced Services Collection for TCP-IHS functionality, which supports the main activities needed to be provided for process coordination and control, is also proposed. Using these pattern solutions and data modeling concepts, appropriate reusable software components can be developed, and some of them already have been implemented successfully in our projects, and we finally introduce some screenshots of our Web-based applications. 1. Information Handling Systems for Technological Process Control – “state of the art”, common features, enabling technologies, and modern trends The technical problem of complex technological processes automated control in the real-time mode remains actual and important nowadays. As the main reasons of such actuality the large time and cost constraints of such systems, as far as the strong requirements to their reliability and stability can be distinguished. Such computerized systems should support such actions as receiving the data from technical controllers and devices, performing the control commands and actions, representing the actual state of controlled technological processes, supporting the decision making process of operating staff, etc. The main distinguishing features of information handling systems for technological process control (TPC-IHC) can be considered as the following: § The architecture of such systems is mostly distributed § The working cycle is continuous (so called “24x7” mode) § The system topology is characterized with the large-scale and multidimensional relationships between several subsystems § The used data resources are heterogeneous § Such systems are supposed to include legacy software applications, as far as additional modules and subsystems § Systems should support the various types of user actors and their groups § The problem of user’s support in some extreme operating cases (the analysis of failures, devices trouble-shooting, ad hoc queries and commands, etc) One of the main international trends in the domain of TPC-IHS development is the usage of SCADA (Supervisory Control Access and Data Acquisition) system concept[1-4]. This class of information handling systems could be considered as an extension of CAD/CAM systems family, determined by hard-ware devices level, which they are interfacing with. Typical SCADA system is a special software solution facilitating a lot of programmable logical controllers (PLCs). The main goal of SCADA system is to collect the technological process data, to represent them in proper time and form, and to accomplish the necessary control actions. According to our investigations and experience, we suppose, that using of Webtechnologies can successfully solve a problem of complex TPC IHS design. Most of all, we are guided by the following reasons and considerations: § The usage of TCP/IP and HTTP protocols allows to solve the problems of distributed applications design and development, and their stable functioning, even in the situation, when communication links and channels have a low capacity and work seesaw § Internet environment shows the best correlation with the paradigm of TPC IHS functioning in the “24x7” mode § Such Web-standards and technologies, as XML, DOM, RDF, and their browser-tier support can provide the heterogeneous data integrated processing in such systems § The server-side and component programming technologies, like ActiveX and ASP (Microsoft Corp.), or EJB and JSP (OMG and Sun Microsystems) can be an effective platform for legacy software integration. 2. TPC-IHS in the Ukrainian Gas-Field Industry – our project description During last 3 years our R&D group has fulfilled a number of projects aimed to the TPC-HIS elaboration for gas-branch enterprises. Some results of these projects were presented in [5-8]. Let’s consider now our applied-oriented approach to design the architecture of Web-based regional information handling system of dispatch control for the gas-productive manufactures in Kharkiv region (Ukraine). Such system will allow: § To provide the continuous and quick access to the required information related to the all technological processes and objects in the regional system. Such access will be possible in the authorized mode from every node of such system, as far as from vehicular communication devices (laptops, mobiles) § To provide the hot link between system users (e.g. operator in gas-extraction node can obtain the technical advise information from an expert in regional management center) § To store, systemize and analyze the all the information, which could be necessary for the preparation and making the day-to-day and strategic decisions, concerning to the technological process control and dispatch reporting During such IHS design and implementation the fundamental principles of modern complex information systems development, such as Open System Architecture – OSI standard, object-oriented analysis and design of the whole system and its separate components structure – OMG and ODMG standards[9], heterogeneous information resource integration, and others, as far as appropriate information technologies for Web-based information systems design and development, including UML as a notation for system structure modeling and complex software design, MS COM+/MS .Net and ASP as component technologies for Web-programming (or their alternatives, such as J2EE and JSP), modern database management systems, such as MS SQL Server 2000 and Oracle 9i, the standards for structuring and processing of large volumes of heterogeneous data resources in Internet/Intranet (XML, RDF, DOM). Usage of these principles and technologies should provide the high scientific and technical level of the project and its implementation, as far as the possibility of continuous and effective system reengineering realization in future. The proposed regional dispatch system has the distributed multilevel network architecture, each level of which will include the Web-oriented software package (WSP), meant for storing, representing and analyzing of technological information. The following levels of the proposed architecture can be distinguished: § Gas Field level – the WSPs of the gas-fields concern to this level. § Sectional level this level represents the organizational union of several neighboring WSPs. § Regional level. The node of this level includes the WSP for top-level branch management, and the main goal of it is to support the decision making process for the whole distributed technological system control. The system architecture described here is open – it means that it is possible to add the new logical levels, from one hand, to cooperate with national and international branch management organizations, and, from other hand, to include some additional intermediate nodes for technological data processing. 3. Architectural Design Patterns Designing such complex IHS, we propose to use the approach, based on the design and elaboration of architectural pattern solutions, and on their basis, reusable software components. It allows to provide the standard way of design and implementation of whole distributed TPC-IHS. We can emphasize the following pattern solutions and their corresponding software components: 1. Integrated Node Database (INDB) – it is used to storing and processing all the information, which is necessary to the WSP functioning. 2. Data Exchange Server (DES) – the component, which supports the data exchange with the controllers of technical devices, which are the components of appropriate system node. 3. Data Visualization Service (DVS) – the set of serverand client-side components, which provide the visualization of technological process. 4. Data Synchronization Service (DSS)– also is represented by the set of serverand client-side components, which are aimed to synchronize the data in the different system nodes. 5. User Accounts Manager (UAM)– this component is necessary for providing the data access rights for the system users. 6. Advanced Services Collection (ASC)– represents simulation models and appropriate software tools and packages for the decision support making. These system architecture components are presented in the form of UML Component Diagram on Fig.2. Sectional Level Node Regional Level Node Gas Field Level Node DSS