YUML and YPL Database Manual

Don Batory
Department of Computer Science
The University of Texas at Austin
Austin, TX, USA

Yuml is a free web service for drawing UML class diagrams given a Yuml input specification. As this is a for-profit company, the "free" service comes with some strings attached. Namely, it will produce a pretty class diagram for you provided that your specification is not too complicated. To familiarize yourself with Yuml:

go to the Yuml Class Diagram Web site
type in this spec

[student|name]has-loves[course|name]

and Yuml returns this gorgeous picture:

Draw some diagrams of your own. When you feel comfortable, proceed to the next section.

Yuml Specifications

A Yuml specification is elegant. Here is a BNF of a subset of Yuml that MDELite uses for class diagrams. Literals (a.k.a. tokens) are in single `quotes'.

// This is a crude grammar for Yuml.
// The Yuml grammar for class diagrams is essentially the following
// (but note, Yuml is more general)

YumlSpec : Line+ ;    // one or more lines

Line: Box | Connection ;

Box : '[' Class ']' ;  

Connection : Box [End1] [Role1] '-' [Role2] [End2] Box ;

End1 : '<>' | '++' | '^' | '<' ;
End2 : '<>' | '++' | '^' | '>' ;

Role1 :  String ;   // String that has no ']' chars

Class : String                         // name only
      | String '|' String              // name and methods only
      | String '|' String '|' String   // name, field, and methods
      ;

Note that a String token is mentioned above. This not a Java String, but one that is devoid of the characters:

comma	,
left brace	[
right brace	]
less than	<
greater than	>
minus	-

Further, a semicolon ";" means new line. Some hints:

As Yuml doesn't like "[]" as in "String[]", I use "#" -- so "String[]" becomes "String#".
As Yuml doesn't like commas (as in "foo(int x, int y)"), I simply use blanks between types -- like "foo(int int)".
As Yuml has no indicator to distinguish static from non-static, I simply preface the names of static members with an underscore -- like "_bar()".

Consider the following Yuml specification:

[interface;Closable|close()]
[interface;NetworkChannel|bind();getLocalAddress();getOption();setOption();supportedOptions()]
[MyClass|_MyClass();close()]
[interface;Closable]^-.-[MyClass]
[YourClass]<>-3>[MyClass]
[interface;Closable]^-[interface;NetworkChannel]

Yuml produces this beauty:

Warning! Do not read the above specification too deeply! 'Interface;Closable' is a String. The word 'Interface' means nothing to Yuml. It could just as well have been 'George', which also means nothing to Yuml. What Yuml does understand is ';' (semicolon), which means add a new line. So 'Interface;Closable' produces a 2-line name in the above figure. And the string 'bind();getLocalAdddress()' means print strings 'bind()' and 'getLocalAddress()' on separate lines.

The YPL Schema

Here is the YPL schema (ypl.schema.pl), which can encode YUML diagrams as a database of tuples:

% yuml class schema

dbase(ypl,[yumlBox,yumlAssociation]).

% type = n (for note), c (for class), i (for interface)
% abst : if type==c, is the class abstract? 
% abstract class names are prefaced by "Abs_"

table(yumlBox,[id,type,"name","fields","methods",abst:bool]).

% end1 = <> | ++ | ^ | < | "" (nothing)
% end2 = <> | ++ | ^ | > | "" (nothing)
% lineType = - | -.-

table(yumlAssociation,[id,box1,"role1","end1","lineType",box2,"role2","end2"]).

Here is a translation of (i.e., the database of tuples that encodes) the specification of the first figure:

dbase(ypl,[yumlBox,yumlAssociation]).

table(yumlBox,[id,type,"name","fields","methods",abst:bool]).
yumlBox(b0,c,'student','name','',false).
yumlBox(b1,c,'course','name','',false).

table(yumlAssociation,[id,box1,"role1","end1","lineType",box2,"role2","end2"]).
yumlAssociation(a0,b0,'has','','-',b1,'loves','').

And here is a MDELite.ClassYumlParser translation of the specification of the second figure:

dbase(ypl,[yumlBox,yumlAssociation]).

table(yumlBox,[id,type,"name","fields","methods",abst:bool]).
yumlBox(b0,i,';Closable','close()','',false).
yumlBox(b1,i,';NetworkChannel','bind();getLocalAddress();getOption();setOption();supportedOptions()','',false).
yumlBox(b2,c,'MyClass','_MyClass();close()','',false).
yumlBox(b3,c,'YourClass','','',false).

table(yumlAssociation,[id,box1,"role1","end1","lineType",box2,"role2","end2"]).
yumlAssociation(a0,b0,'','^','-.-',b2,'','').
yumlAssociation(a1,b3,'','<>','-',b2,'3','>').
yumlAssociation(a2,b0,'','^','-',b1,'','').

Of course, you can take these databases and convert them back into Yuml specs using MDELite.ClassYumlUnParser. See the MDELite Manual for more details.

YPL Constraints

There indeed are YPL constraints. I have not posted them, as they are good examples for homework assignments.