## 2 The Tendency to Increase the Volume and Complexity of Data and Program Collection of the DSS
From the entire previous discussion, it is evident that the information involved in the PCS is huge and very complex [30]. 3. The inclusion and use of data, which are directly or indirectly georeferenced (map-related data), in a DSS. In the first case, the direct one, the exact co-ordinates of an object are explicitly provided. On the contrary, in the second case, the indirect one, there is a link to an object, which determines the data co-ordinates. For example, if an accident takes place at a specific point of a certain road and then, if the exact co-ordinates of the accident location are registered in an IS, this event is directly georeferenced. On the other hand, if the registered information is something like the following: \"the accident happened at the 23 rd kilometer of the road from city A to city B\", then the event is indirectly georeferenced. Usually, the main bulk of the information is indirectly georeferenced. A surprisingly large part of the information that should be included in such a DSS is georeferenced, even though this georeferencing is well hidden at a first glance. For example, in most nations, such as the USA, the laws and directives may drastically change when crossing state boarders. Even in Greece, where the legislation is much more uniform, when one travels from an island to the mainland, one faces various changes in authority jurisdiction and legislation in the interior of the island, the mainland, at ports and on the sea (near-port area, national waters and international waters). It is evident that the requirement that a large-scale decision support system handles and uses map-related information may greatly increase the volume of its data and program core. Finally, special DSS architecture requirements, like the following:  
* Distributed and/or geographically dispersed systems, where properly selected duplication of part of the information and programs must be implemented, in order to increase the efficiency of the local systems. For example, a very frequently accessed part of information by all sub-systems must be preferably kept in every local sub-system. * Umbrella-type systems that receive and process information in real time from a large number of heterogeneous, autonomous and, possibly, legacy systems. Sometimes, these systems may cover a large part or the whole of a continent. Such is the case of a European system for maritime surveillance, the complexity and size of which is evident. Severe Difficulties Appearing in the Actual Deployment of a Very Large-Scale Decision Support System  
We use the general term \"large data collection\" in order to describe the extended data core of a large-scale decision support system. The data collection may include dozens or even hundreds of groups of loosely related data sets or databases, the content of which may be thematically divergent. In this work, we will often use examples of large-scale decision support systems for policy support and decision making in the area of transport. We will do this for two main reasons:  
* In many transport DS systems, practically all problems referred to in the present work have already emerged, due to the huge size and complexity of the involved data. As a first example, we state the large number (more than 50) of Federated States in the USA. An analogous second example is the European Transport Information System, which is a DSS for supporting transport policy decisions in all EU countries. * Engineers and other scientists that have developed the pioneering versions of the transport DS systems have faced a considerable number of serious difficulties and problems, many of which still remain unsolved. It must be emphasized that for a considerable number of these difficulties and problems, the severity of the resulting hazards may be anticipated. We would like to mention the following, widely used terminologies in transport DS systems: The data and program collections are often called \"repositories\", \"observatories\" or \"transport observatories\".