As input into the discussion on Friday, I have tried to give a description of the main problem domain which we are trying to address. After this description, I have tried to define what we understand by site, service, VO and resource based on our experience within this problem domain. Problem Description: Universities and research institutes are real organizations that have computing centers. Each organization is autonomous and have their own, security infrastructure, policies, systems etc. and are ultimately responsible for their resources. Scientists from different institutions collaborate on specific research topics and they would like to use the resources available to them. The difficulties faced by the collaboration is that each organization where the resources are located have different, security infrastructures, policies, systems etc. To solve this problem the security infrastructures, policies, systems need to be generalized. A common security model is adopted where usage of resources at an organization is dependent on the collaboration to which the user is participating. Types of systems are also generalized so that the user does not have to understand the details of different implementations that organizations have. An interface is required at the organizational boundary that maps the generalized system to the organizational specific security model and the local system. Site: A site represents the real organization, eg Universities and Research Institutes which are administrative domains. It is usually a physical location where the resource and system administration team can be found. They have their own polices and identity and exist independently of other sites. Virtual Organization: A virtual organization represents the collaboration, a group of scientist working together for a specific topic. Within this virtual organization there may be sub groups and different roles. Virtual organizations also have there own policies and exist independently. Members of the VO do not have to belong to any organization which provides resources. Service: The service is the interface at the site boundary that maps from a generic grid interface to the local system. As the service provides the interface between the grid and a local system, there is a relationship between the service and the site. In addition there is also a relationship between the service and the virtual organization. Services also have to ensure the adherence to agreed common polices, eg access logs, accounting and auditing etc. Resource: A resource is the functionality that the user would like to use. As the resource is local to the site, there is a relationship between the resource and the site. As the service gives access to the resource there is also a relationship between a resource and a service.