Article Preview
Top1. Introduction
Today, the fast way to contact person or organization became over the Internet by using social networks applications, social interactions over such applications became basic part of our daily activities. Social networks defined as set of nodes and edges, where nodes represent individuals or objects and edges represent the relationships or interactions between nodes (Xu et al. 2016; Rossi et al. 2015). Community is a term used to identify the tendency group of individuals to form condensed interactions and relations between them than individuals not belonging to that group (Bansal et al. 2011; Alzahrani & Horadam, 2016). Community structure used in networks analysis to achieve a specific target (Barabâsi et al. 2002), discover complex networks topology or discover valuable insights from the networks (Hassan et al. 2015). It used to detect groups and subgroups which have similar features (Xu et al. 2015; Kawamoto & Rosvall, 2015). There are several areas affected by community structure such as bio-informatics, sociology and information science (Babers et al. 2015). Several researches analysis complex networks and discover insights in it (Banati & Arora, 2015; Cao et al. 2015; Yu et al. 2015; Azar & Vaidyanathan, 2015; Emary et al. 2014a).
Traditional methods such as graph partitioning used to detect community within networks by dividing it based on predefined size. Spectral clustering method is based on similarity matrix and merging similar groups used by hierarchical clustering method (Choudhury & Paul). Community detection (CD) in social networks is one of the important researches in social networks and graph analysis (Wang et al. 2015). CD based on node centric which nodes in such community satisfy certain properties as degree and reachability, also each group in community satisfy certain condition as density of interaction within nodes in the same group (Azar & Vaidyanathan, 2015; Hassanien et al. 2014).
The network defined as group of objects or entities interact with each other and linked by relationships called edges. Nodes represent anything as person, cell phone, PC’s IP, car and product, the relationships between nodes are the connection linking them. There are different types of connections such that direct and indirect relation. The powerful tool for studying the structure of complex systems is network analysis (Albert & Barabási, 2002; Newman, 2003) which is useful in understanding the interactions and relationships established among nodes (Watts et al. 2002; Lusseau & Newman, 2004; Flack et al. 2006; Hassanien et al. 2015), also in describing and predicting the behavior of nodes.
Social Networks consist of two basics parts which are individuals (nodes) and relationships (edges) and can be defined formally using graph structure, 
where 
is the set of nodes and relations or edges are 
(Hassan et al. 2015). The number of nodes denoted by 
and the number of edges by 
. Given a set of nodes 
, the target is dividing those nodes into groups such that nodes in the same group are related and similar to each other and nodes in different group are dissimilar to each other. The challenge is to detect the number of communities within such complex networks, where each community is fulfilled objective quality function.
(1) Where
is an objective quality function and
is assuming that the quality measure minimized without lose in the context. Measures used for social networks analysis are different and depend on the network size. For example, the measures used: centrality, association index and node degree (Salama et al. 2012; Maharani & Gozali, 2015).