I'm currently playing around with predicates in Alloy. I know that I can use assert and check statements to confirm that my model is working as it should. However, is there any way to check that a predicate I have created has done what I expect? Or do I just have to show the instances and search through them manually?
Just say what you "expect", and set it up as an assertion. Unfortunately, Alloy does not currently have a mind-reading command :-)
Related
I have written in model using Alloy. However for certain conditions running the predicate to find an instance is failing and it says that no instance can be found. I tried increasing the bound to about 16 instances, yet it does not find any instance.
Is there any way I can debug this so that I can see which facts are failing which is causing Alloy not being able to find an instance?
Thanks !
If you change the default sat solver to minisat with unsat core, then it will be possible to highlight the constraints that can't be satisfied in a same instance.
Another possible solution is to comment your constraints one by one until analysis yield an instance hence pinpointing which constraint might cause trouble.
For a more specific answer, please share your model.
I'm learning Alloy, and can use check and run individually. But, when I have them both in, it seems that the check is ignored. How do I execute both the check and the run?
To expand the question:
If I have a run, do I even need a check? Won't it automatically check all my assertions? Or is the goal of the check not only to check the assertions, but to intentionally and exhaustively (within the scope) search for a counterexample?
Is the goal of run only to find an instance that meets the predicate? Or is there another usage of run?
Perhaps check should be search-counterexample and run should be search-example?
Is Alloy limited to one search (check or run) for execution? If so, is the best practice to simply comment out all but one check/run, and uncomment out one at a time?
How do I execute both the check and the run?
You don't. You do one at a time.
Given two predicates P1 and P2, it's always possible to define a new predicate to combine them however you want (with and, or, and not, =>, etc., etc.), and doing so can be very helpful sometimes.
Given a predicate P and an assertion A, however, there may be less need to check them at the same time than you think. If the assertion A holds for a given scope, then it holds whether predicate P is satisfied or not. If it always holds in that scope, then you don't need to check it in addition to P, when seeking an instance of P. (It will hold whether you check it or not.)
If I have a run, do I even need a check? Won't it automatically check all my assertions? Or is the goal of the check not only to check the assertions, but to intentionally and exhaustively (within the scope) search for a counterexample?
An assertion is checked only when you ask the Analyzer to check it. The Analyzer checks the assertion precisely (and only) by looking for counter-examples.
In this, assertions differ from Alloy facts, which are always true by definition (or: by fiat) and need not be checked. (And more than that: they cannot be checked: since a counter-example is impossible, there is nothing for the Analyzer to look for, and there is no verb by means of which you could request that the Analyzer look for it.)
The difference between facts and assertions is worth thinking about.
Facts express constraints on a model; assertions don't. Informally, an assertion can be thought of as a suggestion (or claim) that a given constraint is already imposed on the model, that it follows logically from what has already been said. Assertions which state the blindingly obvious are useful, because checking them can draw our attention to situations where those blindingly obvious things are not in fact true. Assertions which state non-obvious consequences of the constraints in a model are also useful, in a different way, drawing our attention as readers to consequences we might have overlooked.
Facts can be useful too, as simple ways to restrict the model to situations we are interested in. But since they are always true, whether redundant with other constraints or not, facts have fewer opportunities to surprise us. (The most frequent surprise I associate with facts is the unwelcome discovery that my formulation of a fact has made it impossible to find any instances of the model. Over time, I have come to avoid using facts wherever possible: anything I am tempted to write as a fact, I end up rewriting as a predicate.)
Is the goal of run only to find an instance that meets the predicate? Or is there another usage of run?
That's the only one this user of Alloy knows.
Perhaps check should be search-counterexample and run should be search-example?
You may have a point; find-example and find-counterexample might be clearer for new users. (I wouldn't like search here, at least not without -for.) But some users' fingers may rebel at replacing a five-character command like check with a twenty-one-character equivalent.
Is Alloy limited to one search (check or run) for execution? If so, is the best practice to simply comment out all but one check/run, and uncomment out one at a time?
Not necessary; the Execute menu gives you your choice of the command to execute.
I would like to refer to the question that can be found at this address :
Running alloy analyzers in parallel
Is there any ongoing research or conclusion reached on the decomposition of Alloy models, in order to allow a more optimal analysis of models ?
This interests me greatly.
I am very interesting in this topic too. Maybe we can think about it like this. When starting Alloy engine to solve a constraint, we can call a function from Alloy and ask it to solve one constraint. I think we can call this function in cluster mode, and ask each node to solve one constraint. Then, we can compute the subset of the results from each node. See here for example: http://alloy.mit.edu/alloy/code/ExampleUsingTheCompiler.java.html
I am not sure we can work like this, but it's worthy to think about it in MapReduce like framework.
I have a specific scenario as follows:
if (element shows up on UI)
validate it
else
no harm done; move on...
If I know upfront if the element shows up or not, I can frame two different scenarios, when the element shows up and when not.
But, in this case, it may or may not be present. If it is present, it should function as expected.
Any suggestions on how this can be implemented in a Cucumber scenario(s) ?
I am using Cucumber-jvm.
You have two separate scenarios, you just need to be able to make sure you setup the preconditions to assume one scenario vs the other.
In general, you should not be implementing a conditional inside a single scenario, because your intent is to test two scenarios.
I have a requirement to add fields onto a form based on data from another set of entities. Is this possible using an event script or does it require a plugin?
Given that I understand your assignment correctly, it can be done using JavaScript as well as a plugin. There is a significant difference that you need to take into consideration.
Is the change to the other entities to be made only when an actual user loads a form? If so, JS is the right way.
Or perhaps you need to ensure that those values are written even if a console client or system process retrieves the value of the primary entity? In that case, C# is your only option.
EDIT:
Simply accessing the values from any entity in the onload event can be done using a call to oData. I believe someone else asked a similar question recently. The basic format will look like this.
http://Server:Port/Organization
/XrmServices/2011/OrganizationData.svc
/TheEntityLogicalNameOfYoursSet()?$filter=FieldName eq 'ValueOfIt'
Some extra remarks.
If you're targeting on-line installation, the syntax will differ, of course, because the Schema-Server-Port-Organization are provided in a different pattern (https, orgName.crm4.something.something.com etc.). You can look it up on Settings.
Perhaps it should go without saying and I'm sure you realize it but for completeness' sake, TheEntityLogicalNameOfYours needs to be substituted for the actual name (unless that is your actual name, in which case I'll be worried, haha).
If you're new to this whole oData thingy, keep asking. I got the impression that the info I'm giving you is appreciated but not really producing "aha!" experience for you. You might want to ask separate questions, though. Some examples right off the top of my head.
a. "How do I perform oData call in JavaScript?"
b. "How do I access the fetched data?"
c. "How do I add/remove/hide a field programmatically on a form?"
d. "How do I combine data from...?"