# OLGAVis: On-Line Graph Analysis and Visualization for Bibliographic Information Network
## 2 Background and Preliminaries  
### Heterogeneous Information Network  
The information knowledge system can be represented by a number of information knowledge entities, their attributes, and the meaning given to related attributes, description, interaction, and relations. Components that are interconnected and interacting form a type of network, and a system that is based on these relationships and connections, is called information network [1; 2]. Research has been actively performed over recent decades to understand the relevance by representing the interaction between elements constituting the system as relationships, or to analyze the latent patterns and meanings.  
Information networks use graphs to model objects and interactions between objects that constitute a system. More specifically, this network defines a graph G = (V,E) by setting an object as a vertex, and the relationship as an edge, where V refers to a vertex and E refers to an edge. For example, in a bibliographic information service, papers can be represented by a vertex and a reference relationship can be represented by an edge, whereas, in a social network service, a user can be represented by a node, and a friend relationship can be represented by an edge. Individual instances of an object set can have a connection relationship. The relationship between the reference and the referenced is configured as a directed network, and the relationship only representing the presence or absence of the relationship is configured as an undirected network.  
If the objects and relationships constituting the information network have only a single type, then it is called a homogeneous information network [12]. Some of the examples include friendship networks in social networks and author collaboration networks in bibliographic information (Figure 1a). The type of object exists only as unique attributes, such as \"user\" or \"author\", while the edge relationship is represented by single attributes, such as \"are friends\" or \"collaborate\".  
However, in the real world, there are not many networks in which only a single type exists. Even in the case of representing and analyzing the data in an homogeneous information network, most cases focus on the discovery of specific information or knowledge through the process of abstraction or reduction of the real world. For example, there are various types of objects that constitute the bibliographic information system, such as author, paper title, keyword, journal or conference, year and volume, and even an author object can have various attributes, including the author's name and affiliated institution. There are several types of edge relationships because there are various types of objects. The type of edges is highly diverse, depending on the type of relationship between individual instances in an object set, including \"write\", \"reference\", \"publish\", and \"collaborate\" (Figure 1b).  
Accordingly, a network that consists of multiple types of object sets and relationship sets is called a heterogeneous information network [10; 11]. In this system, when there is a demand for analysis with focus on the collaborative relationship between authors, a homogeneous information network analysis is conducted in the case of simplifying and representing only the \"author\" object and the \"collaboration\" relationship, excluding other object attributes, while a heterogeneous information network analysis is conducted in the case of deriving richer semantics for various objects and relationships.