Writing MetaModel Constraints in Java Streams
updates in green

Work in groups of 2 in this assignment.  So find a long-term partner.

A fundamental tenet of future software design is the elevation of programming beyond standard languages like C, C++, C#, and Java.  In Model Driven Engineering, the Object Constraint Language (OCL) is used to define and evaluate metamodel constraints. There are other languages besides OCL.  In this course, we use Java Streams to express constraints.  Java streams exhibit a flavor similar to OCL, but I trust the Java language designers more than I do the OCL designers.

In this assignment, you will write metamodel constraints as Java Streams.  You will need to read a bit about Java Streams to become familar with it. 


1. Read about Java Streams

I gave a short tutorial in class on Java Streams and provided some in-class examples for you to try.  But you still need to brush-up on your knowledge. Listed below are some tutorials that you can consult, (try #1 first).  Frankly, I don't think any of them are particularly good.
  1. https://www.tutorialspoint.com/java8/java8_streams.htm
  2. https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html
  3. http://www.oracle.com/technetwork/articles/java/ma14-java-se-8-streams-2177646.html

2 Install MDELite7 Software

MDELite7 is a fifth-generation of experimental tools for writing MDE applications.  Install MDELite7. (You should have done this in the previous programming assignment). Follow its installation instructions and read its (short) main document.


USE THE VERSION OF VIOLET THAT COMES WITH MDELite7 -- the version that is downloadable from the violet web site is not usable for this assignment. Violet is a Java-based tool that allows you to draw a number of different UML diagrams, including class diagrams, state diagrams, and so on. You can run Violet from MDELite7 by the invocation:
> java MDL.Violet 
Like many drawing tools, Violet is not very smart.  Look at the figure below.  Violet allows you to customize relationships between pairs of classes by drawing lines between boxes.  Once a line is drawn, you can say 'put a diamond at this end of the line', 'put an inheritance arrow at this other end', and so on, yielding a diagram that is UML-like, but nonsensical.  The figure below has several errors:  (1) inheritance links never have diamonds on them, (2) inheritance links don't have labels, and (3) inheritance links between classes are not dashed and are always solid. 

Violet allows you to draw any nonsensical set of beautiful boxes and links, and to output them as an XML documents with a .violet extension.  If you click on the figure above, you will see the XML file that is produced.  I ask you -- who in God's name can read XML?? Continuing, you will also see that Violet is not very good at defining methods and variables -- it only provides a big fat text string in which you can scribble almost anything.  If you click on the figure below, you will see the MDELite Schema for Violet class diagrams and the tuples that define the above class diagram.  Notice that the content of the XML file is minimal in database form.

MetaModel Constraints

In the first part of this assignment, you will write Java Stream expressions to evaluate vpl database constraints. Fortunately, a violet-to-database translator has been written for you.  It is available in the MDELite7 toolset and can be invoked by:

> java Violett.ClassParser X.class.violet X.vpl.pl

and yes, Violett with 2 t's is correct (ask me why in class), where X is the name that you gave to the violet file (its full name is X.class.violet).  Violett.ClassParser is hardcoded to output tuples that conform to the vpl schema (vpl.schema.pl).

Note: what this means is that if the schema is changed, then VioletClassParser must be manually changed.  There is no reason for you to change vpl.schema.pl or Violett.ClassParser in this assignment.

The naming scheme is important: "X.vpl.pl" -- X is as before, vpl is the name of database schema, and "pl" simply designates a fact file.  To test conformance, you will write the following Java program:

> java VPL.Conform X.vpl.pl 

which evaluates the database constraints that you apply to validate all vpl databases.   The way you get started is:

So again, you will (a) translate each of your .class.violet files to a vpl database using the provided MDELite7 tool and (b) write a set of English constraints for vpl databases, (c) translate these constraints into Java Stream expressions (this is your VPL.Conform program), and (d) check whether the .violet diagram conforms to your metamodel constraints.  The next two sections provide background that you need to understand before you can do anything.

VPL Schemas and Databases

Before continuing, you should understand the set of tables that are generated.  The vpl schema consists of 2 tables, namely vBox and vAssociation.  In class, I explained the basic syntax of database schemas and their tuples. Here's the schema:

% vpl class database


% type = c(class),i(nterface),n(ote). packages are skipped

% type1,type2 = c(lass) or i(nterface
% lineStyle = ""(solid) or "DOTTED"
% bentStyle = "", HV, VH, HVH, VHV

Here's what the above means:  

Your Java program, VPL.Conform, evaluates metamodel constraints using Java Streams that will check the correctness of .violet models of class diagrams.  There are all sorts of constraints that you could write on checking the validity of fields and methods. But because Violet simply mashes field and method declarations into a big fat text string, this makes it almost impossible to do fancy checking.  So to keep things simple -- and you should thank me for this --  do NOT write checks about method and field declarations!  Limit yourself to checking the following constraints:
Please check MDELite html documentation for constraints.  There is a class, PrologDB.Constraints, that has a set of methods that can be used to express each of the above constraints in one method call.

In the process of developing VPL.Conform, do the following:
> java MDL.Violet create class diagram X.class.violet
> java Violett.ClassParser X.class.violet X.vpl.pl transform X.class.violet to X.vpl.pl
> java VPL.Conform X.vpl.pl see if X.vpl.pl conforms to constraints

The following zip file contains a set of 8 Violet designs that you are to validate.  For each file, present the list of error messages (if any) that your tool produces.  I presume that you will test your work on other Violet designs.  You should include them in your documentation too.

Start with this "shell" of a NetBeans Project

What to Submit to Canvas

All of the below in a zip file (including your Netbeans or Eclipse Project). The zip file must unzip into <yourName>/<YourFilesAndDirectories>.
  1. Your program needs to run correctly on Linux machines, even though you may have developed them on Macs and Windoze.  The TA will grade your program running on Linux.
  2. Your Java vplConform source.

  3. An easy to read english description of your program -- document anything that you have added beyond what was given in the shell.

  4. For each Violet example, the output of your conformance test and maybe the violet diagram for that example.

  5. A PDF file (in the required format) that the Grader should read to provide any information that is not obvious.  The contents of the PDF file can be minimal.

You should expect other violet files, of the Grader's choosing, will be used to evaluate your rules/constraints.