use activity diagram to model a system

  Only a flavouring.

  I found to use activity diagram to build a system model is a good choice for me.Instead of modeling with sequence diagram,I model another model of filesharing with activity diagram.

  Now I have finished the analysis model,base on this,I will make a design model in my spare time.

NCE L19:can,could,may,might

1.request permission;

polite:can(friends and equals)<could,may<might(superior)

2.may/might + infinitive

  may/might + perfect infinitive

3.may/might as well + infinitive

  for example:

  I might as well play game( as learn english-it makes no difference).

"have" and "have got"-L18

  When "have" expresses the meaning of "possess",it equal to "have got".

  For example:

  This sock has (got) a hole in it.

  This room has (got) four windows.

  But in the sentence below,it cann't be replaced by "have got":

  They had a good time at the party.

  its meaning is:to enjoy or suffer;experence,often as part of a group

  At this viewpoint,"have" is a unversal word.for example:have meal,have letter,have a look,have it...

  We can view these in LONGMAN dictionary.p701-702

NCE L17:"must" versus "have (got) to"

  There are two way in "must".

  First,it says:this is your necessity,you have to face it.at this meaning,it has no PAST tense and FUTURE tense itself.

  PAST TENSE:I had to do it.

  FUTURE TENSE:I will have to do it.

  Second,it says:this is your obligation.This is a deduction.at this meaning,it can express a past action: (modal + perfect inifitive) He must have done it.

  Another point:

  I have to do it.(no contraction)

  I've got to do it.(the contraction is always used)