Usability and Privacy Aspects of Moodle: Students' and Teachers' Perspective

State Machine, ASM for short, is a powerfulcomputational model [34], which has been successfullyapplied in several cases for modeling critical, complexsystems, both in industry and in academia: widediscussion about ASM application is in [7]. It simulatesevery algorithm’s behavior through a step-by-step way:each step computes a set of updates with given transitionrules. After the completion of a step, all updates arecommitted simultaneously.The concept of abstract state in ASM extends theusual notion of state occurring in Finite State Machines:it is an arbitrarily simple or complex structure, i.e. acollection of domains, with arbitrary functions andrelations defined on them. On the other hand, rules arebasically nested if-then-else clauses with a set offunctions in their bodies. In each state, all conditionsguarding rules are checked, that is all rules whoseconditions are evaluated to true are simultaneouslyexecuted, so determining the state transition. All theparameters are stored in a set of so called locations and ateach time the particular configuration of parametersvalues determines the current state of the ASM.The transition from one state to another is describedthrough a set of formulas, in the form:{if conditioni then updatesi} i = 1,..,nwhere each conditioni (the guard of the i-th rule) is anarbitrary first-order formula, whose interpretation can betrue or false, and each updatesi is a finite set ofassignments f(t1,...,tn) = twhose execution is to be understood as changing thevalue of the function f at the given parameters ti, thatleads to a new value of the parameter t. The parametersare stored in a set of locations and the configuration ofparameter values at each step determines the current state of the ASM.For the unambiguous determination of a next state, itis necessary that updates are consistent. An update set isconsistent if it contains no pair of updates which assigndifferent values to the same location; otherwise, theupdate set is inconsistent.The concepts related to modeling monolithic systemsthrough ASMs can be extended to distributed systems.The case of job management in Grid systems is a typicalcase of asynchronous distributed systems. It is distributed because its overall behavior is thecomposition of different, independent, remote elements,each operating on its own. It is asynchronous because allinvolved logical components operate and communicateconcurrently, each according to its internal behavior. So,job EMSs in Grid can be modeled by a DistributedAsynchronous ASM asyncASM [7], [21].Essentially, asyncASMs generalize simple ASMs toan arbitrary finite number of independent agents [23],each executing an ASM in its own local state. Formally,an asyncASM is given by a family of pairs (a, ASM(a)) ofpairwise different agents, elements of a possibly dynamicfinite set Agent, each executing its ASM, ASM(a). In thissense, each agent a executes its own program, operating 298 Informatica 37 (2013) 295–306A. Bianchi et al. on its own states, so determining a partial view of theentire system. The relation between global and localstates is supported by the reserved keyword self, used todenote the specific agent executing a rule, and to storeinformation relevant to itself. A new agent can beintroduced into the asyncASM at any time by extendingthe set Agent.An ASM-based process for developing complexsystems is presented in [7]: it allows capturing systemmodel requirements and refining them throughintermediate models to any desired level of detail in avalidated and verifiable code. In the present work,modeling and implementation activities have beencarried out with the support of the coreASM framework[8], [9], [22]. It follows mathematical definition of ASMsand inherits several typical features of the ASMmodeling. Its main purpose is to make ASM-basedmodels executable. To this end, the framework includessome language constructs aimed at making easy thedevelopment, as, for instance, forAll, which allowsexecuting all rules satisfying a given guard condition;choose, aimed at expressing non-determinism in thechoice of a rule to execute when a condition is satisfied; seqblock/endseqblock are the delimiters of block, whoserules must be executed sequentially; par/endpar are thedelimiters of block, whose rules must be executedconcurrently; enqueue/dequeue are the operators foradding / removing elements to a queue. 4 Modeling the Grid job EMSs In order to model the job EMSs, firstly the Gridcapabilities and features are informally described, thenthey are abstracted and formally defined, finally the asyncASM is created in the coreASM environment [8]. 4.1 Informal description of a Grid system