initial project
add compiled clss file, fixed .gitignore file
just a test for eclipse plugin
delete class files
add basic frame of program

Former-commit-id: 482a069f3c581709ae4d105ad0173e1e22cc3fbd
add basic frame of program
add Package DAO, Class Datum, Tuple, Operator, ScanOperator

Former-commit-id: feff635953f775d4927834820c9e43e9936f13e3
add Package DAO, Class Datum, Tuple, Operator, ScanOperator
fixed and tested ScanOperator.java,
it can be used now.

Former-commit-id: 69f1ce7a898e75206714c377db84511ab9a97f86
fixed and tested ScanOperator.java,
it can be used now.
add SelectionOperator, Evaluator
not tested, incomplete implementation

Former-commit-id: 21f859f675a3c38eb15cdc730af01d0caa5af212
add SelectionOperator, Evaluator
not tested, incomplete implementation
fully implemented selectionOperator,
not tested


Former-commit-id: 13f029ebf47aaaa72a84109916a05b37e6f27b72
fully implemented selectionOperator,
not tested
complete projection

Former-commit-id: 23a0d0c554ea0c0519a67bf68d6f7786117638cf
complete projection
aggregate function : count, sum

Former-commit-id: 945f8024e03f0ea3d181909cc9b12296bebb4f99
aggregate function : count, sum
aggregator

Former-commit-id: 2103aaa4a0a2401330cf3db2da4f545c278d4207
aggregator