arXiv subjects

Pietro Hiram Guzzi

Publications and source records attributed to Pietro Hiram Guzzi.

25 records · Page 2Linked to original sources

arXiv2020

Using Network Embeddings for Improving Network Alignment

Network (or Graph) Alignment Algorithms aims to reveal structural similarities among graphs. In particular Local Network Alignment Algorithms (LNAs) finds local regions of similarity among two or more networks. Such algorithms are in general based on a set of seed nodes that are used to grow an alignment. Almost all LNAs algorithms use as seed nodes a set of vertices based on context information (e.g. a set of biologically related in biological network alignment) and this may cause a bias or a data-circularity problem. More recently, we demonstrated that the use of topological information in the choice of seed nodes may improve the quality of the alignments. We used some common approaches based on global alignment algorithms for capturing topological similarity among nodes. In parallel, it has been demonstrated that the use of network embedding methods (or representation learning), may capture the structural similarity among nodes better than other methods. Therefore we propose to use network embeddings to learn structural similarity among nodes and to use such similarity to improve LNA extendings our previous algorithms. We define a framework for LNA.

cs.SI↗

arXiv2020

Top-k Connected Overlapping Densest Subgraphs in Dual Networks

Networks are largely used for modelling and analysing data and relations among them. Recently, it has been shown that the use of a single network may not be the optimal choice, since a single network may misses some aspects. Consequently, it has been proposed to use a pair of networks to better model all the aspects, and the main approach is referred to as dual networks (DNs). DNs are two related graphs (one weighted, the other unweighted) that share the same set of vertices and two different edge sets. In DNs is often interesting to extract common subgraphs among the two networks that are maximally dense in the conceptual network and connected in the physical one. The simplest instance of this problem is finding a common densest connected subgraph (DCS), while we here focus on the detection of the Top-k Densest Connected subgraphs, i.e. a set k subgraphs having the largest density in the conceptual network which are also connected in the physical network. We formalise the problem and then we propose a heuristic to find a solution, since the problem is computationally hard. A set of experiments on synthetic and real networks is also presented to support our approach.

cs.DS↗

arXiv2020

Extracting Dense and Connected Subgraphs in Dual Networks by Network Alignment

The use of network based approaches to model and analyse large datasets is currently a growing research field. For instance in biology and medicine, networks are used to model interactions among biological molecules as well as relations among patients. Similarly, data coming from social networks can be trivially modelled by using graphs. More recently, the use of dual networks gained the attention of researchers. A dual network model uses a pair of graphs to model a scenario in which one of the two graphs is usually unweighted (a network representing physical associations among nodes) while the other one is edge-weighted (a network representing conceptual associations among nodes). In this paper we focus on the problem of finding the Densest Connected sub-graph (DCS) having the largest density in the conceptual network which is also connected in the physical network. The problem is relevant but also computationally hard, therefore the need for introducing of novel algorithms arises. We formalise the problem and then we map DCS into a graph alignment problem. Then we propose a possible solution. A set of experiments is also presented to support our approach.

cs.DS↗

arXiv2016

Learning Weighted Association Rules in Human Phenotype Ontology

The Human Phenotype Ontology (HPO) is a structured repository of concepts (HPO Terms) that are associated to one or more diseases. The process of association is referred to as annotation. The relevance and the specificity of both HPO terms and annotations are evaluated by a measure defined as Information Content (IC). The analysis of annotated data is thus an important challenge for bioinformatics. There exist different approaches of analysis. From those, the use of Association Rules (AR) may provide useful knowledge, and it has been used in some applications, e.g. improving the quality of annotations. Nevertheless classical association rules algorithms do not take into account the source of annotation nor the importance yielding to the generation of candidate rules with low IC. This paper presents HPO-Miner (Human Phenotype Ontology-based Weighted Association Rules) a methodology for extracting Weighted Association Rules. HPO-Miner can extract relevant rules from a biological point of view. A case study on using of HPO-Miner on publicly available HPO annotation datasets is used to demonstrate the effectiveness of our methodology.

q-bio.QM↗

arXiv2016

The impact of Gene Ontology evolution on GO-Term Information Content

The Gene Ontology (GO) is a major bioinformatics ontology that provides structured controlled vocabularies to classify gene and proteins function and role. The GO and its annotations to gene products are now an integral part of functional analysis. Recently, the evaluation of similarity among gene products starting from their annotations (also referred to as semantic similarities) has become an increasing area in bioinformatics. While many research on updates to the structure of GO and on the annotation corpora have been made, the impact of GO evolution on semantic similarities is quite unobserved. Here we extensively analyze how GO changes that should be carefully considered by all users of semantic similarities. GO changes in particular have a big impact on information content (IC) of GO terms. Since many semantic similarities rely on calculation of IC it is obvious that the study of these changes should be deeply investigated. Here we consider GO versions from 2005 to 2014 and we calculate IC of all GO Terms considering five different formulation. Then we compare these results. Analysis confirm that there exists a statistically significant difference among different calculation on the same version of the ontology (and this is quite obvious) and there exists a statistically difference among the results obtained with different GO version on the same IC formula. Results evidence there exist a remarkable bias due to the GO evolution that has not been considered so far. Possible future works should keep into account this consideration.

q-bio.QM↗

arXiv2014

A web-based tool to Analyze Semantic Similarity Networks

In computational biology, biological entities such as genes or proteins are usually annotated with terms extracted from Gene Ontology (GO). The functional similarity among terms of an ontology is evaluated by using Semantic Similarity Measures (SSM). More recently, the extensive application of SSMs yielded to the Semantic Similarity Networks (SSNs). SSNs are edge-weighted graphs where the nodes are concepts (e.g. proteins) and each edge has an associated weight that represents the semantic similarity among related pairs of nodes. The analysis of SSNs may reveal biologically meaningful knowledge. For these aims, the need for the introduction of tool able to manage and analyze SSN arises. Consequently we developed SSN-Analyzer a web based tool able to build and preprocess SSN. As proof of concept we demonstrate that community detection algorithms applied to filtered (thresholded) networks, have better performances in terms of biological relevance of the results, with respect to the use of raw unfiltered networks.

cs.CE↗

arXiv2013

Thresholding of Semantic Similarity Networks using a Spectral Graph Based Technique

Semantic similarity measures (SSMs) refer to a set of algorithms used to quantify the similarity of two or more terms belonging to the same ontology. Ontology terms may be associated to concepts, for instance in computational biology gene and proteins are associated with terms of biological ontologies. Thus, SSMs may be used to quantify the similarity of genes and proteins starting from the comparison of the associated annotations. SSMs have been recently used to compare genes and proteins even on a system level scale. More recently some works have focused on the building and analysis of Semantic Similarity Networks (SSNs) i.e. weighted networks in which nodes represents genes or proteins while weighted edges represent the semantic similarity score among them. SSNs are quasi-complete networks, thus their analysis presents different challenges that should be addressed. For instance, the need for the introduction of reliable thresholds for the elimination of meaningless edges arises. Nevertheless, the use of global thresholding methods may produce the elimination of meaningful nodes, while the use of local thresholds may introduce biases. For these aims, we introduce a novel technique, based on spectral graph considerations and on a mixed global-local focus. The effectiveness of our technique is demonstrated by using markov clustering for the extraction of biological modules. We applied clustering to simplified networks demonstrating a considerable improvements with respect to the original ones.

q-bio.MN↗