uml - Can a use case be without an actor? -


i working on use case diagram of automated system. external system trigger 1 use case of system. of other use cases scheduled tasks , invoked timer. have use case invoked timer , includes , extends 2 other use cases.

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when write use case discriptions, actor uc-2 , uc-3. can use case exists without actor? have seen lot of use case diagrams has included or extended use cases without directly conneced actor. please clarify this. in advance.

edit: system connected dbms. system analyse database workload time time , check whether tuning can done. that's system. uc-1 analyse dbms, uc-2 check performance statistics , uc-3 tune database. timer 1 invoke use case. dbms gets benefit.steps in check performance (uc-2) repeated in use case. that's why put separate use case. on other hand tune database(uc-3) performed if there need tuning after analyzing database.

officially correct. included use case mandatory part of including use case , extending use case optionally extend use case. @ister notes in comment, actor included/extending use cases of main use case.

but, , experience, best avoid use of include/extend relations. in cases, people tend use them functional decomposition plain wrong. use case shall show added value actor, not how piece of functionality used somewhere. in cases structuring of added value not present , can show each bubble stand-alone use case or integrate main use case. recommend reading bittner/spence matters.

edit1: realize sentence

trigger 1 use case of system

this rather sounds mix use cases activities. it's not piece of functionality. use case added value. there scenario (set) use case has trigger. saying "a use case triggered" sounds wrong. trigger activities of use case (where starts getting technical). techies have difficulties making cut , abstract use cases. 1 more reason read bittner/spence.

edit2: in comment talking technical use cases. admit had intensive discussions in past. need differentiate between technic , business. business use cases analyse dbms, check performance, , tune database. such no ucs timer institution cares performance. uc timer trigger task (or that). there cut. timer not care business. happily trigger shutdown of system in same way. not become business actor fact technically used start business relevant process.

and not forget: read bittner/spence. me book eye opener since had no idea intention of use cases.


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