root/gaphor/tags/gaphor-0.12.3/doc/items.tex

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\title{Gaphor Diagram Item Model}
\author{wrobell@pld-linux.org}

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\begin{document}
\maketitle

\chapter{Basic Classes of Diagram Items}
\section{Introduction}
UML specification defines UML data model, which is used by Gaphor to store
information about a modeled system. The UML data model is visualized by
the Gaphas library, a general purpose diagram drawing library. Notation
of UML diagram items is also specified by the UML specification.

The Gaphas library supports basic drawing operations but there are many
entities and behaviors, which are common to many or all diagram items, i.e.
stereotypes, item name, popup menu, positioning of associated items, etc.

We have to identify common elements and behaviors of UML diagram items
and define basic diagram items classes, which will be used
by Gaphor to provide modeling functionality.

Note that, the diagram item hierarchy does not have to follow the hierarchy
defined in the UML model. 

\section{Problem Description}

\subsection{Items and Diacanvas}\label{gaphor:basic:itemsandcanvas}
Diacanvas library supports different canvas objects
\begin{itemize}
\item canvas element
\item canvas line
\end{itemize}

Because of differences between them, Basic diagram item class cannot be
directly associated with canvas lines or canvas elements. Connection between
canvas classes and items has to be established by different abstract
classes.

\subsection{Items and UML Model Classes}
Generaly there is a one to one association between an item and an UML class,
but it is not always that simple. 
For example one diagram item can visualize more than one UML class
\begin{itemize}
\item decision node item can represent combined decision and merge nodes
\item fork node item can represent combined fork and join nodes 
\end{itemize}

Also, there can be situation, when there is no UML class visualized, i.e.
in case of a CommentLine.

\subsection{Line Items}
Lines have at least two handles. These handles are reffered to as head (first
handle) and tail (last handle) of line.

When a user puts an item on a diagram, then the last handle can be moved to
a desired point. The same applies to line items. User puts a line on diagram,
head is set in mouse cursor point and tail is moved to desired point.

Head and tail concepts are also used in Gaphas in case of canvas lines.
Head of line item is at the same end as head of canvas line. The same
applies for tail.

\subsection{Item Styles}\label{itemstyles}
All the items are going to contain different parts.
Many of such parts can be shared by other items, for example
\begin{itemize}
\item UML named elements (see named items) have names, which
    can be displayed in different places, i.e. class --- top--center,
    use case --- middle--center
\item every UML class can have stereotypes, which should be displayed
    over items' name
\end{itemize}

Above can be described as styles (i.e.\ similar to CSS).

It should be possible to implement common behaviour in basic item classes,
which should be parametrized by item's style information. For example,
named element item should set position of name depending on styles.

\section{Styles}
Class \rclass{ElementItem} defined below should define following styles
\begin{description}
\item[min--size] minimal size of an item; minimal width and height are
    initialized using this style information
\end{description}

\section{Classes}
\rclass{DiagramItem} class is a basic, abstract class for all items. Every
item class is created using \rclass{DiagramItemMeta} metaclass.

Different canvas elements (see~\ref{gaphor:basic:itemsandcanvas}) are
supported with classes
\begin{itemize}
\itemsep0pt
\item \rclass{LineItem}
\item \rclass{ElementItem}
\item \rclass{FeatureItem}
\end{itemize}

\begin{class}{DiagramItemMeta}
\begin{attrs}
\iattr{\_\_uml\_\_}{UML class associated with item}
\iattr{\_\_stereotype\_\_}{item static stereotype}
\iattr{\_\_style\_\_}{used to define new and override item style information}
\iattr{style}{used to obtain item style information, also information derived from base classes}
\end{attrs}
\begin{entitydesc}
Metaclass for all items. Assigns information about UML class, stereotypes,
styles, etc.\ to every item class.
\end{entitydesc}
\end{class}

\begin{class}{DiagramItem}
\begin{attrs}
\iattr{subject}{reference to UML class instance}
\iattr{popup\_menu}{item popup menu definition, i.e. rename, delete, etc.}
\end{attrs}
\begin{entitydesc}
Basic class for all diagram items.
\end{entitydesc}
\end{class}

\begin{class}{LineItem}
\begin{attrs}
\iattr{head}{reference to head handle of a line}
\iattr{tail}{reference to tail handle of a line}
\end{attrs}
\begin{entitydesc}
Canvas line based items like dependencies, association, flows, message, etc.
\end{entitydesc}
\end{class}

\begin{class}{ElementItem}
\begin{attrs}
\iattr{min\_width}{minimal item width}
\iattr{min\_height}{minimal item height}
\end{attrs}
\begin{entitydesc}
Canvas element based items like class, component, lifeline,
comment, activity nodes, etc.

Minimal width and height are initialized from minimal size style
information. These two values can change during item lifecycle (i.e.\ name
can be expanded or shrinked), therefore minimal size style information
guards initial minimal dimensions of element item.
\end{entitydesc}
\end{class}

\begin{class}{FeatureItem}
\begin{entitydesc}
Canvas element, which is part of an item. For example represents
attributes and methods of classes.
\end{entitydesc}
\end{class}

\section{Methods}
\begin{method}{DiagramItem.set\_subject}
\begin{attrs}
\iattr{subject}{reference to UML class instance}
\end{attrs}
\begin{entitydesc}
assign UML class instance to an item
\end{entitydesc}
\end{method}

\chapter{Align of Item Elements}
\section{Introduction}
\begin{figure}
\begin{center}
\includegraphics[width=.5\textwidth]{flow}
\end{center}
\caption{Flow Item example}\label{items:example:flow}
\end{figure}

Many items consist of several elements, for example flow item is a line
with
\begin{itemize}
\item stereotype
\item name
\item guard
\end{itemize}
These elements are aligned to a line of flow (see
figure~\ref{items:example:flow})
\begin{itemize}
\item stereotype is near one of the ends of line
\item name is under stereotype
\item guard is near the middle of line
\end{itemize}

Element of items are aligned according to attributes of
\rclass{ItemAlign} and \rclass{LineAlign} classes. Align information is
assigned to every item element, but position is calculated from item
perspective, for example
\begin{itemize}
\item align of an element to the (left, top) with margin $(10, 15, 15, 5)$
puts an element in (left, top) corner of item; it is located $10px$ from the top
and $5px$ from the left of item
\item align of an element as above but outside item puts an element $10px$
from top and $5px$ from the left of item; top and left margin values are
used for top vertical and left horizontal align
\end{itemize}
See figure~\ref{items:align} for more examples.

\begin{figure}
\begin{center}
\includegraphics[width=.95\textwidth]{align}
\end{center}
\caption{Align of Item Elements}\label{items:align}
\end{figure}

Align constants and classes are defined in \rmodule{gaphor::diagram::align} module.

\subsection{Stereotype and Name Alignment}

There are two important elements of items
\begin{itemize}
\item every item shown on diagram has stereotype (even item for Stereotype
    UML class, which stereotype is \rstereotype{stereotype})
\item many items has names
\end{itemize}

Therefore every item class has \rattr{s\_align} attribute, which defines
align of stereotypes.

Named items are aligned according to \rattr{n\_align} attribute. If
stereotype and name align values are the same, then name is put
centered under stereotype.

\warning{What about FeatureItem stereotype?}

\chapter{Named Items}
\section{Problem Description}
Named items represent those UML classes, which derive from NamedElement.

All named items are editable, so user can double click on an item and
change or enter name of UML object.

There should be minimal size (which is default, initial one) of named
items. Every named item can have its own minimal size. Size of named item
can be changed by an user. There are some cases, when size cannot be
changed, i.e. initial node item.

It should be possible to align name of named element with styles
(see~\ref{itemstyles}) as depending on an element, the name can be
displayed in different places related to an item, i.e.
\begin{itemize}
\item class               --- top center
\item use case            --- middle center
\item object node         --- middle center
\item actor               --- bottom center, outside item bounduaries
\item initial action node --- top left, outside item bounduaries
\item decision node       --- bottom center, outside item bounduaries
\end{itemize}

%fixme: there can be items with initial name and without initial name

\section{Styles}
Kind of information we need to align the name
\begin{itemize}
\item horizontal align information (left, center or right)
\item vertical align information (top, middle or bottom)
\item padding specified as in CSS (top right bottom left)
\item is name outside an item?
\end{itemize}

Styles for name align are defined in table~\ref{nameditems:styles:spec}
(see diagram~\ref{nameditems:styles:example} for example).

\begin{table}
\begin{center}
\begin{tabular}{|l|l|l|}
\hline
Name           & Default value     & Description \\
\hline
name--align    & ('center', 'top') & align information \\
name--padding  & (5, 5, 5, 5)      & name padding \\
name--outside  & False             & name outside/inside item bounduaries \\
\hline
\end{tabular}
\caption{Specification of name align styles}\label{nameditems:styles:spec}
\end{center}
\end{table}

\begin{code}
\lstset{language={Python}}
\begin{pylst}
class NamedItem(DiagramItem):
    __style__ = {
        'name-align' : ('center', 'top'),
        'name-padding': (5, 5, 5, 5),
        'name-outside': False,
    }
\end{pylst}
\caption{Named items style example}\label{nameditems:styles:example}
\end{code}

\section{Classes}
Class NamedItem is a base class for all named items.

\begin{class}{NamedItem}
\begin{entitydesc}
Calculates minimal size based on name size. Draws UML object's name using
style information.
\end{entitydesc}
\end{class}

%%%
%We have to distinguish between two kind of named elements. One is related
%to canvas elements and second is related to canvas lines. For example, name
%of UML object can be positioned inside or outside canvas element (class vs.
%initial node), also name can be centered or on left/right side of canvas
%element. In case of canvas line based items name can be near head, tail
%or centre of a line and name can be put horizontaly or along line path.
%%%


%\subsection{Canvas Element Named Items}

%\subsection{Canvas Line Named Items}

\chapter{Relationships}

Relationships are implemented using Python descriptors. See Relationship,
DependencyRelationship and AssociationRelationship classes for examples.

\chapter{Profiles}

\section{Gaphor Stereotypes}

\begin{description}
\item[name] UML class of an item derives from NamedElement; name
        should be shown on diagram
\item[nostereotype] item does not allow to edit stereotypes
\end{description}

\section{Diacanvas Stereotypes}

\begin{description}
\item[editable] item is editable when it is possible to change name of an
    item by clicking twice on it
\end{description}


%fixme: chapter below should be chapter with number
\chapter{Glossary}

\begin{description}
\item[static stereotype] stereotype, which is always assigned
    to an item; for example interface item is annotated with
    \rstereotype{interface} stereotype

\item[item] item put on diagram by user, i.e. ClassItem, AssociationItem;
    conforms to UML notation of UML metamodel classes

\item[UML class] class defined in UML metamodel
\end{description}

\end{document}