Recommender systems are increasingly driving user experiences on the Internet. This personalization is often achieved through the factorization of a large but sparse observation matrix of user-item feedback signals. In instances where the user's social network is known, its inclusion can significantly improve recommendations for cold start users. There are numerous ways in which the network can be incorporated into a probabilistic graphical model. We propose and investigate two ways for including a social network, either as a Markov Random Field that describes a user similarity in the prior over user features, or an explicit model that treats social links as observations. State of the art performance is reported on the Flixster online social network dataset.

The trend towards more complex software within today's technical systems results in an increasing demand for dependable high quality software for real-time systems. In this report the foundations for the compositional pattern-based design of correct high level designs and architectures for real-time systems are presented. A formal calculus including a notion of discrete-time automata, a deadlock preserving refinement notion, and a class of supported compositional constraints is developed. It permits to design the required complex cooperation between the system components using verified patterns and includes support to derived the related correct component behavior in a systematic manner, such that the components itself do not invalidate the verified cooperation patterns.

State-of-the-art object-oriented analysis and design combined with techniques handling concurrency and distribution on the design level ease the development of distributed systems. A novel approach and language for the visual design of distributed software systems is introduced and illustrated by means of an example. The language of OCoNs (Object Coordination Nets) integrates the structuring mechanisms of object-oriented concepts which are crucial for handling complex software systems with the graphical expressive power of Petri-Nets for describing concurrency and coordination. The same visual language is used to specify the interfaces of software components, the resource handling within a component as well as the control flow in methods.

For distributed object or component systems based on CORBA or DCOM, a suitable software architecture and a strong separation of modules is necessary. Current visual notations have several drawbacks: concurrency support is very limited and they fail to integrate the external state based view of objects when aspects of data and control flow are specified. Hence, they are not sufficient to support a seamless contract based design style. Our object coordination net approach (OCoN) allows mixed event and state based true concurrent modeling. It describes contracts, object scheduling, resource handling and the abstract data and control flow of services. A seamless integration of contract specifications into service and object scheduling specifications is provided. Although abstract, the OCoN formalism remains operational which permits abstract simulation and a feasible implementation is guaranteed. The report compares the OCoN approach with current design notations and illustrates its benefits by means of an extended example.

ARRAY(0x56451dffe3a8)

ARRAY(0x5627fe4aa360)

The UML as standardized language for visual object-oriented modeling allows to capture the requirements as well as the structure and behavior of complex software systems. With the increasing demands of todays systems, behavior aspects like concurrency, distribution and reactivity become more important. But the language concepts of the UML for describing behavioral aspects are weak compared to its concepts for describing structures. Besides a lack of visual expressiveness, a deeper integration with the structure specification is missing. In order to close this gap, an expressive language for modeling object-oriented behavior is proposed with the OCoN approach. It describes contracts, object scheduling as well as control and data flow of services in a Petri-net-like form. A seamless visual embedding of contract specifications into service and object scheduling specifications is provided by different net types.