Trigger Inheritance and Overriding in an Active Object Database System
An active database is a database in which some operations are automatically executed when specified events happen and particular conditions are met. Several systems supporting active rules in an object oriented data model have been proposed. However, several issues related to the integration of triggers with object oriented modeling concepts have not been satisfactorily addressed. We discuss issues related to trigger inheritance and refinement in the context of the Chimera active object oriented data model. In particular, we introduce a semantics for an active object language that takes into account trigger inheritance and supports trigger overriding. Moreover, we state conditions on trigger overriding ensuring that trigger semantics is preserved in subclasses.

title: A temporal authorization model
abstract: This paper presents a discretionary access control model in which authorizations contain temporal information. This information can be used to specify temporal intervals of validity for authorizations and temporal dependencies among authorizations. A formal definition of those concepts is presented in the paper, in terms of their interpretation in first order logic. We characterize sets of temporal dependencies that can lead to undesirable states of the authorization system and we sketch an algorithm for their detection. Finally, operations to add, remove, or modify authorizations and temporal dependencies are described.

title: Extending the ODMG Object Model with Time
abstract: Although many temporal extensions of the relational data model have been proposed, there is no comparable amount of work in the context of object-oriented data models. Moreover, extensions to the relational model have been proposed in the framework of SQL standards, whereas no attempts have been made to extend the standard for objectoriented databases, defined by ODMG. This paper presents T_ODMG, a temporal extension of the ODMG-93 standard data model. The main contributions of this work are, thus, the formalization of the ODMG standard data model and its extension with time. Another contribution of this work is the investigation, on a formal basis, of the main issues arising from the introduction of time in an object-oriented model.

title: Extending the ODMG object model with composite objects
abstract: In this paper we extend the ODMG object data model with composite objects. A composite object is an object built by aggregating other component objects. Exclusiveness and dependency constraints, as well as referential integrity, can be associated with composition relationships among objects. Our composite object model is developed in the framework of the ODMG object database standard data model, but can be used in both object-oriented and object-relational database systems. In the paper, we propose a language for defining composite objects and we define the semantics of update operations on composite objects.

title: An Approach to Authorization Modeling in Object-Oriented Database Systems
abstract: Authorization is an important functionality that every data management system should provide. An authorization mechanism allows different access rights on data items to be selectively assigned to users. Authorization models and mechanisms have been widely investigated in the framework of traditional database systems. The extension of those models and mechanisms to advanced data management systems is quite complex, because those systems are characterized by data models with a larger number of semantic constructs than traditional models, like the relational one. A first authorization model defined for object-oriented (and semantic) database systems has been presented in . In this paper we present an authorization model that substantially extends and revises that model. The most significant extension concerns the support for content-dependent authorization, which was not provided in . Content-dependent authorization is very important in providing an authorization mechanism able to directly support authorization policies of application environments. Moreover, it is a crucial functionality in environments where data objects frequently change their status. In addition, the model presented here differs from the model defined in [20] in that new authorization types are introduced and a finer control of versions is provided. Finally, authorization administration of objects is considered.

title: An index allocation tool for object-oriented database systems
abstract: The problem of index configuration is an important topic for database system performance and has been extensively investigated for relational Database Management Systems (DBMS). By contrast, the problem of index allocation for Object-Oriented DBMS (OODBMS) has been considered only from a theoretical point of view and no practical development of any tool for commercial OODBMS has been reported. In this paper, we investigate the problem of index configuration in the framework of a commercially available OODBMS. We first identify the features that characterize such OODBMS and we develop two cost models: the first extends the generic cost model presented by Gardarin et al. (), the second is an analytical cost model tailored to the OODBMS at hand. Both cost models have been validated by comparing the estimated costs and the actual costs observed from the system. The comparison has shown that both models are quite accurate. Using the proposed cost models, we have also developed an algorithm for the efficient index allocation on a given path, given a workload specified in terms of operation frequencies. Even though our algorithm has been developed for a specific OODBMS, we believe that it can be easily tailored to other OODBMS and persistent programming languages.

title: Access control enforcement for conversation-based web services
abstract: Service Oriented Computing is emerging as the main approach to build distributed enterprise applications on the Web. The widespread use of Web services is hindered by the lack of adequate security and privacy support. In this paper, we present a novel framework for enforcing access control in conversation-based Web services. Our approach takes into account the conversational nature of Web services. This is in contrast with existing approaches to access control enforcement that assume a Web service as a set of independent operations. Furthermore, our approach achieves a tradeoff between the need to protect Web service's access control policies and the need to disclose to clients the portion of access control policies related to the conversations they are interested in. This is important to avoid situations where the client cannot progress in the conversation due to the lack of required security requirements. We introduce the concept of k-trustworthiness that defines the conversations for which a client can provide credentials maximizing the likelihood that it will eventually hit a final state.

title: GEO-RBAC: a spatially aware RBAC
abstract: Securing access to data in location-based services and mobile applications requires the definition of spatially aware access control systems. Even if some approaches have already been proposed either in the context of geographic database systems or context-aware applications, a comprehensive framework, general and flexible enough to cope with spatial aspects in real mobile applications, is still missing. In this paper, we make one step towards this direction and we present GEO-RBAC, an extension of the RBAC model to deal with spatial and location-based information. In GEO-RBAC, spatial entities are used to model objects, user positions, and geographically bounded roles. Roles are activated based on the position of the user. Besides a physical position, obtained from a given mobile terminal or a cellular phone, users are also assigned a logical and device independent position, representing the feature (the road, the town, the region) in which they are located. To make the model more flexible and re-usable, we also introduce the concept of role schema, specifying the name of the role as well as the type of the role spatial boundary and the granularity of the logical position. We then extend GEO-RBAC to cope with hierarchies, modeling permission, user, and activation inheritance.

title: An integrated approach to federated identity and privilege management in open systems
abstract: Online partnerships depend on federations of not only user identities but also of user entitlements across organizational boundaries.