==== Specification_v1 - Semester 1 ====
=== Node ===
  * Ordinary node with text title
  * Audio/Video/Image node
  * Drawing node
  * Tag enable
  * Resizeable
  * Different shape
=== Linkage ===
  * Non-directional
  * Using straight line in this phase
  * Multiple links between the same two nodes is possible
  * Tag enable
=== Tag ===
  * Different shape
  * Coloring
  * Text discription
=== Save/Load ===
  * Not yet decide since there is implementation issue, need further study to decide
  * Text base (xml or custom form)
  * Using CoreData?
=== Control ===
  * Some of the control may be add/remove if there are changes in the UI design
  * Drag to move nodes
  * Pinch to zoom in/out
  * Create nodes by double click with the help of UI (choosing between different kind of nodes)
  * Delete nodes by double click with the help of UI
  * Create linkage by tap once on the original node and hold for a few seconds, then drag a line to the new node