Abstract
The massive growth of the Internet and its services is currently being sustained by the mercantilization of users' identities and private data. Traditional services on the Web require the user to disclose many unnecessary sensitive identity attributes like bankcards, geographic position, or even personal health records in order to provide a service. In essence, the services are presented as free and constitute a means by which the user is mercantilized, often without realizing the real value of its data to the market. In this chapter the auhors describe OFELIA (Open Federated Environment for Leveraging of Identity and Authorization), a digital identity architecture designed from the ground up to be user centric. OFELIA is an identity/authorization versatile infrastructure that does not depend upon the massive aggregation of users' identity attributes to offer a highly versatile set of identity services but relies instead on having those attributes distributed among and protected by several otherwise unrelated Attribute Authorities. Only the end user, with his smartphone, knows how to aggregate these scattered Attribute Authorities' identity attributes back into some useful identifiable and authenticated entity identity that can then be used by Internet services in a secure and interoperable way.

Abstract
Matrix Decomposition methods are applied to a wide range of tasks, such as data denoising, dimensionality reduction, co-clustering and community detection. However, in the presence of boolean inputs, common methods either do not scale or do not provide a boolean reconstruction, which results in high reconstruction error and low interpretability of the decomposition. We propose a novel step decomposition of boolean matrices in non-negative factors with boolean reconstruction. By formulating the problem using threshold operators and through suitable relaxation of this problem, we provide a scalable algorithm that can be applied to boolean matrices with millions of non-zero entries. We show that our method achieves significantly lower reconstruction error when compared to standard state of the art algorithms. We also show that the decomposition keeps its interpretability by analyzing communities in a flights dataset (where the matrix is interpreted as a graph in which nodes are airports) and in a movie-ratings dataset with 10 million non-zeros.

Abstract
A Subgraph Census (determining the frequency of smaller subgraphs in a network) is an important computational task at the heart of several graph mining algorithms. Here we focus on the g-tries, an efficient state-of-the art data structure. Its algorithm makes extensive use of the graph primitive that checks if a certain edge exists. The original implementation used adjacency matrices in order to make this operation as fast as possible, as is the case with most past approaches. This representation is very expensive in memory usage, limiting the applicability. In this paper we study a number of possible approaches that scale linearly with the number of edges. We make an extensive empirical study of these alternatives in order to find an efficient hybrid approach that combines the best representations. We achieve a performance that is less than 50% slower than the adjacency matrix on average (almost 3 times more efficient than a naive binary search implementation), while being memory efficient and tunable for different memory restrictions. © Springer-Verlag Berlin Heidelberg 2016.

Abstract
The industry of video games is one of the fastest growing sectors in the worldwide economy. One of the key factors to increase engagement and player retention, was the use of various common game concepts such as leaderboards and achievements. The massive use of this approach and the impressive growth of players led to the concept of gamification as a service, later materialized in Game Backend as a Service (GBaaS). Instead of replicating the implementation of the game features in each version of the game for several platforms, GBaaS adhere to a service oriented architecture providing cross-platform game services that lets you easily integrate popular gaming features such as achievements, leaderboards, remote storage and real-time multiplayer in games. This chapter surveys several GBaaS based on the features they offer and on their openness for the integration with computer programming environments.

Abstract
Today we use the Web for almost everything, even to program. There are several specialized code editors gravitating on the Web and emulating most of the features inherited from traditional IDEs, such as, syntax highlight, code folding, autocompletion and even code refactorization. One of the techniques to speed the code development is the use of snippets as predefined code blocks that can be automatically included in the code. Although several Web editors support this functionality, they come with a limited set of snippets, not allowing the contribution of new blocks of code. Even if that would be possible, they would be available only to the code's owner or to the editors' users through a private cloud repository. This paper describes the design and implementation of Sni'per, a RESTful API that allows public access for multi-language programming code-blocks ordered by popularity. Besides being able to access code snippets from other users and score them, we can also contribute with our own snippets creating a global network of shared code. In order to make coding against this API easier, we create a client library that reduces the amount of code required to write and make the code more robust. © Ricardo Queirós and Alberto Simões;licensed under Creative Commons License CC-BY.

Abstract
Computer technologies are forever evolving and it is vital that computer science educators find new methods of teaching programming in order to maintain the rapid changes occurring in the field. One of the ways to increase student engagement and retention is by integrating games into the curriculum. Gamification-Based E-Learning Strategies for Computer Programming Education evaluates the different approaches and issues faced in integrating games into computer education settings. Featuring emergent trends on the application of gaming to pedagogical strategies and technological tactics, as well as new methodologies and approaches being utilized in computer programming courses, this book is an essential reference source for practitioners, researchers, computer science teachers, and students pursuing computer science.