3. According to lecture notes on Page 2, what is social network? Why is the positioning a major factor in mobile social network service?

Social Network =經典定義為“分享共同興趣的人群集合。
”具體的定義︰
“The personal or professional set of relationships between individuals. Social networks represent both a collection of ties between people and the strength of those ties. Often used as a measure of social “connectedness”, recognizing social networks assists in determining how information moves throughout groups, and how trust can be established and fostered.”