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74 Integrating Airport Information Systems Weaknesses Because the data are not stored in a central location, how much and how historic data are cap- tured is up to the original software. Thus, queries and analyzing past data can be a problem. Performance can be a problem because each system is last accessed in real-time. Configuration of the EII system (deciding where data comes from, which data to ignore, etc.) can be complicated. Enterprise Application Integration This strategy links various software systems to form a single, integrated system. This type of integration is on the far end of the integration spectrum, integrating not just data but systems and processes. From the viewpoint of a user, systems integrated using EAI can appear to be a single piece of software, although multiple different software systems are behind the scenes. Think of an EAI system as a large Broadway production. A member of the audience (user) sees a coordinated performance of people, props, lights, and sound (various software systems). From the audience point of view, it seems like everything is coordinated perfectly according to plan. Back stage, a director (EAI software) is making sure that the people in charge of the cast, lighting, sound, and props are all coordinated properly. Technologies often associated with EAI software are Web Services and Service Oriented Archi- tecture (SOA). These technologies are used to provide integration, not just at the data level, but at the functional level. For example, business processes might dictate that a specific action in the accounting system (marking an account as delinquent) causes an action in the operations system (marking all work orders for that account as on hold). Web services that allow manipulation of work orders in the operations system might be used to accomplish this kind of integration. Some of the strengths and weaknesses of EAI are as follows: Strengths. EAI is the strongest form of integration techniques because it leads to what appears to be a single system from the user's perspective. Weaknesses. In most cases, EAI is the most complex integration approach and is usually cost prohibitive or impossible with old or proprietary systems; also, because of its ambitious nature, EAI is the most risky integration approach. Integration Technologies This section describes technologies that an airport enterprise can use to implement a chosen systems integration strategy: Relational Database, Online Analytical Processing, Open Database Connectivity and Java Database Connectivity, Flat Files, Extensible Markup Language, and Web Services. Relational Database A relational database is the most common type of database in use today. A relational database is normally built using a Relational Database Management System (RDBMS). Data in a relational database is stored in tables. A table in a relational database is like a spreadsheet, with columns to define the attributes for each data point and each row representing a data point. Another important aspect of relational databases is their ability to enforce constraints on the data (ensures validity of the data) as well as referential integrity (ensuring that tables that refer to each other are consistent).

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Architecture, Strategies, Technologies, and Contracts 75 Online Analytical Processing OLAP is an approach to provide quick answers to queries of multidimensional data (data about more than one facet of an item, such as name, address, city, and state rather than simply a name). To facilitate these queries, OLAP data are organized into multidimensional OLAP cubes that aggregate the facts across the different dimensions of the cube. For example, a sales data cube could be created with dimensions including sales date, region, and product category. The facts contained in this cube could include quantity sold, dollar amount sold, and gross margin. This cube would enable someone to very quickly answer questions like the following, which can take quite a bit of processing power and development time on a relational database: What were the top selling product categories in the east region in Q4? What product categories increased in sales from Q3 to Q4? Did the product categories that increased do so in all regions? The users of OLAP data are typically business people looking for answers on what is going on in their business. Most OLAP software is meant to enable those business people to find the answers themselves, bypassing the need for IT staff to write complex queries. Open Database Connectivity and Java Database Connectivity ODBC and JDBC are standard APIs for accessing data stored in RDBMS. Although ODBC was meant to work with any programming language, JDBC is an API specifically for the Java pro- gramming language. Flat Files A flat file, or text file, is a simple mechanism for storing data that can only be last-accessed sequentially, or from beginning to end. Flat files originated in the early days of software devel- opment, but are still used primarily for importing and exporting data between different systems. Extensible Markup Language XML is a markup language used to describe data. The primary use of XML is to facilitate the sharing of data among software systems. XML has gained wide use on the Internet and is the basis of many other technologies, including Extensible Hypertext Markup Language (XHTML), Really Simple Syndication (RSS), and Extensible Stylesheet Language (XSL). XML schemas are a way to specify validation rules for XML documents. For example, an XML schema can specify that an order document contains at least one order line. U.S. Government standards for XML include the Federal XML Developers Guide and the Federal XML Group Update.2 Web Services Web services are XML APIs that can be accessed over a network, commonly using the World Wide Web Consortium (W3C) standard, Simple Object Access Protocol (SOAP). Web serv- ices differ from traditional APIs in that, due to their use of XML and HyperText Transfer Pro- tocol (HTTP), web services can be used to communicate between software on different operating systems. 2 U.S. Federal Chief Information Office (CIO) Council. Draft XML Developers Guide. Architecture and Infrastruc- ture Committee, XML Working Group, April 2002.