Abstract: This paper analyzes the limitations of current SCADA system information integration in the power market environment, and introduces Service-Oriented Architecture (SOA) technology based on XML Web services into it. An SOA-based SCADA system dispatching platform architecture is designed to realize distributed service function interaction. Keywords: SOA, SCADA system, XML, Web service 0 Introduction Dispatch automation systems utilize computer, communication, and control technologies to collect, monitor, and control data from equipment under the jurisdiction of the dispatch center, achieving functions such as automatic measurement, automatic signaling, automatic control, and automatic regulation. They mainly consist of modules for data acquisition and monitoring, state estimation, security analysis, power flow optimization, and economic dispatch. With the development of power grid technology and computer technology, dispatch automation systems need to integrate hardware devices, operating systems, database platforms, and network protocols from different vendors. This heterogeneity poses serious problems to the interoperability, compatibility, and upgrade capabilities of application software, resulting in numerous scattered and heterogeneous "information silos." To address this phenomenon, this paper proposes a distributed architecture based on SOA for the application of dispatch automation systems. 1. Introduction and Limitations of Current SCADA Systems The development of SCADA systems has progressed from centralized to open and then to distributed systems. To date, the dispatch system of the power grid energy management system has gone through three generations. The structures of these three generations can be summarized into three types: host terminal structure, client-server structure (C/S structure), and functionally distributed structure, as shown in Figures 1-a, 1-b, and 1-c. Currently, the C/S structure is widely used. The traditional client/server (C/S) architecture is an extension of the previous single-machine system, solving the problems of execution efficiency and simultaneous use by multiple users. While this model has advantages such as information dissemination and data distribution via network, a user-friendly interface, distributed management for load balancing, and high cost-effectiveness, some drawbacks have gradually emerged after a period of use and promotion. These include different applications using different client software, resulting in a large maintenance workload; each upgrade requires updating all clients; most applications rely on specific system development platforms, leading to poor portability and scalability, resulting in insufficient flexibility and an inability to meet the urgent requirements of expanding application scale and integrating various software, as well as adapting to complex and changing software and hardware environments. To address these issues, improvements were made to the original system architecture, leading to the emergence of a distributed multi-tier application architecture. The biggest advantage of this architecture is the separation of the user presentation layer, business logic layer, and data layer, making each layer independent. The presentation layer is responsible for the user interface and external interface logic, the business logic layer is responsible for core business rules and business logic, and the data layer is responsible for reading and updating data in storage—the so-called three-tier architecture. The scheduling automation system must not only fulfill monitoring requirements but also interconnect and interoperate with other application subsystems, such as the security analysis subsystem and the optimization and economic scheduling subsystem. The traditional client/server model is inadequate for this. However, the distributed object model provides a standard for interconnecting and interoperating application systems in a distributed heterogeneous environment, enabling the system to offer both high openness and scalability, facilitating the expansion of new application modules. 2. Overview of SOA and Web Service Technologies SOA (Service-Oriented Architecture), as shown in Figure 2, is an architecture that refers to the functional units of an application as services, which are connected through well-defined interfaces and contracts. Interfaces are defined in a neutral manner, independent of the hardware platform, operating system, and programming language used to implement the service. Services map to business functions, and the components implementing services typically map to business entities and the business rules that operate them. The software entities implementing services are usually coarse-grained, loosely coupled, and based on a message communication model. Web services provide support for distributed systems; their platform and language neutrality makes cross-platform interoperability and system integration easier, and the maturity of the technology has led to the widespread application of SOA architectural concepts. From the perspective of the standards jointly negotiated by several major software vendors currently researching and applying these technologies, Web Service technology is undoubtedly the most convenient. The key technologies of Web Service are as follows. [align=center] Figure 2 SOA Architecture[/align] 2.1 SOAP Simple Object Access Protocol SOAP (Simple Object Access Protocol) executes and calls communication between services. Once a Web service is built, SOAP provides a standard RPC method to call it when needed. The SOAP specification defines the format of SOAP messages and how to use SOAP via the HTTP protocol. It is based on XML, inheriting the openness and extensibility of XML, and can solve the consistency problem between multiple applications. 2.2 XML XML is the core foundational technology of web services, the key to SOAP implementation, the basic format for representing data in the Web service platform, and the data encoding method for Web service communication protocols. Its main advantage is platform independence. XML solves the problem of data representation, but it does not define a standard set of data types, nor does it explain how to extend these data types. The XML Schema (XSD) standard developed by the W3C is a standard specifically designed to solve this problem. It defines a standard set of data types and provides a language to extend these data types. 2.3 WSDL WSDL (Web Service Description Language) is a standard for describing web services using XML documents. It's an interface definition language for web services, jointly proposed by Ariba, Intel, IBM, and MS. WSDL describes three basic attributes of a web service: • What the service does – the operations (methods) the service provides; • How to access the service – the data format and necessary protocols for interaction with the service; • Where the service is located – the protocol-related address, such as a URL. WSDL makes it possible to describe services and allows clients to invoke these services in a standard way without needing to know more about underlying protocols such as SOAP and HTTP. 2.4 UDDI UDDI (Universal Description, Definition, and Integration) is used to publish and find services. Users can register their services on the platform so that other users can access them. The directory entry is a document describing the service and how it is provided. The directory also contains methods for searching for the services users need, providing information, contact details, and links to technical data to meet service requirements. Meanwhile, through the provided standard interfaces, users can publish their own services for other entities to call, query the description information of specific services, and dynamically bind to those services. 3. Overall Architecture Design of the SOA-Based Dispatch System The first layer is the power information system layer, which separates basic services that implement certain business functions from each existing information system (EIS) according to service contracts. At the information system layer, the enterprise's existing EIS is encapsulated into one or more basic Web services, providing a unified interface (such as one or more WSDLs). The interfaces originally exposed in various API forms are redescribed using WSDL, and then HTTP + SOAP message transmission is used as a bridge for interaction with the outside world. The system functions that can be divided in the SCADA dispatch system include: message processing, data acquisition, data maintenance, substations, and monitoring. The second layer is the transport layer, which uses an Enterprise Service Bus (ESB) as the "bridge" for transport connection services. The standard-based connection services provided by the ESB can transform the functions or data resources implemented in the application into services that service requesters can access in a standard way. The service provider first publishes the web service it provides to the enterprise's private UDDI, and configures some basic metadata on the ESB, such as the web service container type and invocation method (dynamic/static). When a web service is requested, the ESB provides the web service as a function to the system that needs to use it. Each function is identified by a unique identifier. The system only needs to send a standard SOAP message for the web service's data interface to the ESB, and the ESB will automatically execute the web service and send the processing result back to the requesting system. The third layer is the service layer. The original enterprise application system usually provides fine-grained API interfaces. After web encapsulation, the API is redescribed using XML-based WSDL. This basic service is still fine-grained, while SOA requires service units to be coarse-grained. The basic services are recombined in the service layer to give the services a certain degree of coarse-grainedness. SCADA system basic services include network management services, security services, and data services. The fourth layer is the business layer. In this layer, various encapsulated services are used to build specific business processes in the power system. The fifth layer is the presentation layer, which exposes the service interfaces to customers or partners, provided in the form of web services. [align=center] Figure 3 Structure diagram of SCADA scheduling system based on SOA[/align] 4 Conclusion This paper introduces the application of Service-Oriented Architecture (SOA) in SCADA. It adopts XML-based Web Service technology to achieve seamless connection and integration between heterogeneous systems. The traditional tightly coupled system architecture is used inside the system, while a loosely coupled system architecture is used between the systems. This can maintain the independent integrity of the internal system of the homogeneous system, and realize the communication and integration of heterogeneous systems to form a whole, realize the sharing and integration of power information, and promote the application and management level of power system information integration. References 1 Yang Pu, You Dahai, et al. Implementation of XML Web services in SCADA system. Journal of Electric Power System and Automation. Vol. 15, No. 4, August 2003 2 Ma Lina, Yuan Jinsha, et al. Research and implementation of power enterprise application integration technology based on Web services. Electric Power System Communication. 2005, (11). 3 Gui Youwu, Huang Yanbo. Framework design for enterprise integration using SOA and Web services. Information Technology. 2007, (10) 4 Xu Weibing, Sun Zuo, Chen Jijun. Research on power system information integration based on service-oriented architecture (SOA). China Instrumentation. 2007, (6) 5 Dong Wenwei. Research on distributed Web application system based on SOA. Master's thesis of Northwestern Polytechnical University. 2007 6 Wu Jiaju, Liu Gang, et al. Research on service-oriented architecture based on Web services (SOA). Modern Electronics Technology. 2005, (14) 7 Song Chaoqing. Constructing SCADA system network model using distributed component object model. Automation of Electric Power System. 2000, (9) 8 Ling Xiaodong. Overview of SOA. Computer Applications and Software. 2007, (10)