== How to Implement Parameter Catalogs with Eclipse
:imagesdir: ParameterCatalogs2Images

To build a new parameter catalog from scratch, we first have to understand some basics about Eclipse, and then install the correct Eclipse package.
Thereafter, we can model our data with Ecore considering some best practices, followed by the generation of Java classes and user interface (UI).
We, then, will add some plug-ins to "pimp" our Eclipse installation, (a) to enable deployment of parameter catalog applications, and (b) to add units and quantities to the mix.
Some hints on special modeling problems and versioning parameter catalogs conclude this how-to guide.

=== Eclipse Basics

https://en.wikipedia.org/wiki/Eclipse_(software)[Eclipse] was originally developed by IBM and became Open Source in 2001.
It is best known for its Integrated Development Environments (_Eclipse IDEs_), not only for Java, but also for C++, Python and many other programming languages.
These IDEs are created on top of the Eclipse Rich Client Platform (Eclipse RCP), an application framework and plug-in system based on Java and OSGi.
Eclipse RCP is foundation of a plethora of general-purpose applications, too.

First time users of Eclipse better understand the following concepts.

.Eclipse Packages

An Eclipse package is an Eclipse distribution dedicated to a specific type of task.footnote:[The notion of an Eclipse package has nothing to do with Java packages.]
A list of packages is available at https://www.eclipse.org/downloads/packages/[eclipse.org].
Beside others it contains _Eclipse IDE for Java Developers_, _Eclipse IDE for Scientific Computing_, and the package we will use: _Eclipse Modeling Tools_.
Note that third parties offer many other packages, e.g. _GAMA_ for multi-agent-simulation or _Obeo Designer Community_ for creating Sirius diagram editors.

[NOTE]
====
Several Eclipse packages can be installed side by side, even different releases of the same package. Multiple Eclipse installations can run at the same time, each on its own _workspace_ (see below).
====


.Plug-ins / Features

An installed Eclipse package consists of a runtime core and a bunch of additional plug-ins.
Technically, a plug-in is just a special kind of Java archive (JAR file) that uses and can be used by other plug-ins with regard to OSGi specifications.
Groups of plug-ins that belong together are called a _feature_.

Often, a user will add plug-ins or features to an Eclipse installation to add new capabilities.
E.g. writing this documentation within my Eclipse IDE is facilitated by the plug-in https://marketplace.eclipse.org/content/asciidoctor-editor[Asciidoctor Editor].
Plug-ins can easily be installed via main menu command `Help → Eclipse Marketplace...` or `Help → Install New Software...`.
Some plug-ins may be self-made like our plug-in `de.hftstuttgart.units` that enables Ecore to deal with quantities.
These may be provided via _Git_ or as download and have to be added to an Eclipse installation manually.

  
.Git

https://git-scm.com[Git] is the industry standard for collaborative work on, and versioning of, source code and other textual data.
Collaborative development of parameter catalogs benefits massively from using Git.
Git support is built into _Eclipse Modeling Tools_, the Eclipse package we will use.
However, if Eclipse needs to connect to a Git server that uses SSH protocol (not HTTPS with credentials), access configuration is more involved and may be dependent on your operating system.

Some users, anyway, prefer to use Git from the command line or with one of the client application listed https://git-scm.com/downloads/guis[here], e.g. https://tortoisegit.org[TortoiseGit] for Windows.

While it is required to get Git working at some point, we won't refer to it in this document and, for now, do not cover the installation of Git on your machine or configuration of Git in Eclipse.

.Workspaces

When you start a new Eclipse installation for the first time, you are asked to designate a new directory in your file system to store an _Eclipse workspace_.
Eclipse is always running with exact one workspace open.
As the name implies, a workspace stores everything needed in a given context of work, namely a set of related projects the user is working on as well as meta-data like preference settings, the current status of projects, to do lists, and more.
In case a user wants to work in different contexts, e.g. on different tasks, command `File -> Switch Workspace` allows to create additional workspaces and to switch between them.

[NOTE]
====
Any plug-in from the original Eclipse package or installed by the user later will be copied into the Eclipse installation directory, *not* in any workspace.
Configuration and current state of plug-ins, on the other hand, are stored in workspaces.
====


.Projects

An Eclipse project is a technical term for a directory that often contains:

* files of specific types for source code, scripts, XML files or other data
* build settings, configurations
* dependency definitions (remember the dependencies between plug-ins above?)
* other Eclipse projects.

`File -> New -> Project...` offers many different types of projects that the user can choose from, e.g. Java projects to create Java programs, Ecore modeling  projects, or general projects, that simple hold some arbitrary files.footnote:[Projects possess one or more _natures_ used to define a project's principal type.]

[WARNING]
====
Files that do not belong to a project are invisible for Eclipse!
====

The projects belonging to a workspace can either be directly stored within the workspace as sub-directories (the default offered to the user when creating a new project), or linked from it, that is the workspace just holds a link to the project directory that lives somewhere in the file system outside of the workspace.
Linking allows to work with the same projects in different workspaces.

While it sometimes makes sense to share or exchange workspaces between users,footnote:[Or even work on the same workspace provided in the cloud, see https://www.eclipse.org/che/technology/[Eclipse Che].], I do not recommend this for now.
Projects, in contrast, are shared between users most of the time, usually via Git.
In general, I would suggest to store Eclipse projects outside workspaces at dedicated locations in the user's file system.
That way, we can follow the convention that local Git repositories should all be located under 
`<userhome>/git`.


=== Setup Eclipse Modeling Tools

.Install Java

Eclipse runs on 64-bit versions of Windows, Linux, and macOS and requires an according Java Development Kit (JDK), version 11 or higher, to be installed on your machine.
Even if such JDK already exists, please download OpenJDK, version *15* or newer for your operating system from https://adoptopenjdk.net[AdoptOpenJDK].
footnote:[AdoptOpenJDK recently joined the Eclipse foundation and soon will change its name to _Adoptium_ for legal reasons.]
Choose `HotSpot` as Java Virtual Machine.
Installation process is straight forward, but you can also find links to exhaustive instructions for your operating system.

New Java versions appear every six months, so one could tend to stick with older version 11 that comes with long time support (LTE) until version 17 arrives in autumn 2021.
However, actual version 15 conforms to the latest security measures built into macOS Catalina, so it is a must if software we build here shall be deployed to these systems, too.

Note that different versions of Java coexist peacefully.


.Install Eclipse Modeling Tools

Now its time to download and install the correct Eclipse package _Eclipse Modeling Tools_, version 2020-09 or newer.footnote:[Please stay away from version 2020-03 and 2020-06 of Eclipse Modeling Tools, since these came with a bug preventing the user from editing data in table cells within the generated UI.]
Please go to https://www.eclipse.org/downloads/packages[Eclipse download page for packages].
On this page you may see _"Try the Eclipse Installer"_ or similar.
Do *not* follow this advice, since we want more control over what versions of Java and Eclipse shall be installed.
Instead, look for package _Eclipse Modeling Tools_ and follow the link for your operating system on the right:

.Download links for Eclipse Modeling Tools package
image::EclipseDownload.gif[EclipseDownload, role="thumb"]

Finally, you can click on `Download` and wait for the 400 something MB package to arrive.

[NOTE]
====
Depending on the operating system, several security dialogs have to be acknowledged during installation and first launch of Eclipse.
====

The downloaded installation file contains the application simply named `Eclipse` ready to be copied into `Applications` on macOS or be installed in `Programs` on Windows.
Since later you may add other Eclipse packages -- or different versions of the same package -- I suggest to rename the application more significantly to `EclipseModeling2009` or similar.

After installation has finished launch Eclipse for the first time and you will see a dialog for choosing a new empty directory as its workspace.  

.Initial Dialog to Choose a Workspace Directory
image::SelectWorkspaceDirectory.gif[SelectWorkspaceDirectory, 500, role="thumb"]

Again, more workspaces might come into existence later, so replace the proposed generic directory path and name with a more specific one, e.g.`EclipseModelingWS`.
The Eclipse main window appears with a Welcome Screen open.
It contains links to exhaustive documentation on concept, features and usage of Eclipse that might be of interest later, especially:

* Overview
** Workbench basics
*** Concepts: features, resources, perspectives, views, editors
*** Opening perspectives and views
*** Installing new software manually
** Team support with Git
* Learn how to use the Ecore diagram editor
* Launch the Eclipse Marketplace

For now, you can dismiss the welcome screen. It can be opened anytime by executing `Help -> Welcome`.
Now you should see the initial layout of Eclipse with _Model Explorer_ and _Outline_ on the left and a big empty editing area to the right with a _Properties_ view below.


=== Modeling Parameter Catalogs for Simulation with Ecore
[quote,Phil Karlton / N.N.]
____
There are two hard problems in computer science: cache invalidation, naming things, and off-by-1 errors.
____

It takes time and effort to come along with good names for model entities, projects, files, and so on.
Also, specific naming conventions are in place to enhance readability of models and program code.
Since it is not always clear where names provided during modeling are used later, I compiled a list of names important in Ecore projects and added examples and comments to elucidate their meaning and naming conventions.

.Naming
[width="100%",options="header"]
|====================
| Name             | Demo Catalog Example           | Real World Expample 
| Namespace URI    | http://example.org/democatalog | http://hft-stuttgart.de/buildingphysics 
| Namespace Prefix | democat                        | buildphys 
| Base Package (reverse domain)footnote:[https://en.wikipedia.org/wiki/Reverse_domain_name_notation]
                   | org.example                    | hft-stuttgart.de 
| Main Package     | democatalog                    | buildingphysics 
| Eclipse Projectfootnote:[https://wiki.eclipse.org/Naming_Conventions#Eclipse_Workspace_Projects]
                   | org.example.democatalog        | de.hft-stuttgart.buildingphysics 
| Class Prefix     | Democatalog                    | Buildingphysics 
| XML File Suffix  | democatalog                    | buildingphysics 
| Classes          | e.g. SolarPanel                | e.g. WindowType 
| Attributes       | e.g. nominalPower              | e.g. id
| Associations     | e.g. solarPanels               | e.g. windowTypes 
|====================

Classes are written in https://en.wikipedia.org/wiki/Camel_case[Camel case notation] starting with an upper case letter. Associations and attributes are written the same way, but starting with a lower case letter.

All other names should be derived from the globally unique _name space_ of the project, in our example: `example.org/democatalog`.
It consists of a global unique domain name and a path to the project, unique within that domain.

Use the names of example _Demo Catalog_ to create your first Ecore modeling project:

. Execute `File -> New -> Ecore Modeling Project` from main menu -- not `Modeling Project`!
. Name the project `org.example.democatalog` and uncheck `Use default location` so that the new project is *not* stored in workspace but a different directory you create/choose, then click `Next >`
. Provide `democatalog` as main Java package name, uncheck `Use default namespace parameter` and provide `http://example.org/democatalog` as _Ns URI_ and `democat` as  _Ns prefix_
. Click `Finish`.

Eclipse should look like below with an new empty graphical Ecore diagram editor opened.
The diagram is automatically named `democatalog` after the package name for the Java classes that will be generated from it (provided above).
The _Model Explorer_ shows the contents of the new Ecore modeling project.

.New Ecore Modeling Project
image::DemoCatalogEmpty.png[DemoCatalogEmpty, role="thumb"]

To get your feet wet, do this:

. Drag a _Class_ from the palette on the right onto the editor's canvas: it will materialize as a rectangle labeled `NewEClass1`.
. The class symbol should be selected initially, so you can see its attributes in the _Properties_ view.
. In there replace `NewEClass1` by `EnergyComponentsCatalog` to rename the class.
. Click anywhere on the canvas and notice that the class symbol is deselected and the toolbar at the top adapts accordingly.
. In the toolbar change `100%` to `75%` to scale diagram.
. Execute `File -> Save` to save model and diagram on disk.
. Close diagram editor `democatalog` by closing its tab.
. Reopen saved diagram by double click on entry `democatalog` in _Model Explorer_. 

Technically, everything is in place now to begin modeling the data that the projected catalog shall contain.
Except ... understanding the basics of object-oriented modeling would be helpful.
This is why developers should support domain experts at this stage.

.Model Data with Class Diagrams

Ecore diagrams are simplified UML class diagrams.
Here some resources on what this is all about:

* http://www.cs.toronto.edu/~sme/CSC340F/slides/11-objects.pdf[Toronto Lecture on Object Oriented Modeling]
* http://agilemodeling.com/artifacts/classDiagram.htm[UML 2 Class Diagrams: An Agile Introduction]
* https://www.amazon.de/UML-Classroom-Einführung-objektorientierte-Modellierung-ebook/dp/B00AIBE1QA/ref=sr_1_2?__mk_de_DE=ÅMÅŽÕÑ&dchild=1&keywords=UML&qid=1585854599&sr=8-2[UML @ Classroom: Eine Einführung in die objektorientierte Modellierung (German Book)]

[TIP]
====
Beginners are strongly encouraged to read the first two resources.
The first one contains a gentle introduction, especially suited for domain experts.
The second one can also serve as reference.
====

We will touch central object-oriented concepts _Class_, _Object_, _Attribute_, _Association_, _Composition_, and _Multiplicity_ in an example below, but work through above sources to get a deeper understanding and to enhance your modeling skills.

Note that above sources differentiate between _conceptual_ and _detailed_ models.
All in all we go for detailed models, since only these contain enough information to generate code.
Having said this, it is usually a good idea to have two or three conceptual iterations at a white board to agree on the broad approach before going too much into detail.
But even if one starts with Ecore models right away, these also can be adapted any time to follow a new train of thought.

See here the essential and typical structure of a parameter catalog in a class diagram.
Instead of artificial example classes like _Foo_ and _Bar_ it shows classes from an existing catalog, albeit in very condensed form.

.Principle Structure of a Parameter Catalog
[plantuml, role="thumb"]
----
together {
  class SolarPanel
  class Inverter
}

class EnergyComponentsCatalog {
    author: String
}

abstract class EnergyComponent {
    modelName: String
    revisionYear: int
}

abstract class ChemicalDevice {
    installedThermalPower: double
}

abstract class ElectricalDevice {
    nominalPower : double
}

class Boiler {
    type : BoilerType
}

class CombinedHeatPower {
    thermalEfficiency : double
    electricalEfficiency : double
}

class Manufacturer {
    name : String
}

enum BoilerType {
  LowTemperature
  Condensing
}

class SolarPanel {
    mppVoltage : double
    mppCurrent : double
}

class Inverter {
    maxDCVoltage : double
    maxDCCurrent : double
}

BoilerType -[hidden]- Boiler

ElectricalDevice --|> EnergyComponent
SolarPanel --|> ElectricalDevice
Inverter --|> ElectricalDevice
ChemicalDevice --|> EnergyComponent
Boiler --|> ChemicalDevice
CombinedHeatPower --|> ChemicalDevice

EnergyComponentsCatalog *-- "0..*" Inverter: inverters
EnergyComponentsCatalog *-- "0..*" SolarPanel: solarPanels
EnergyComponentsCatalog *-- "0..*" Boiler: boilers
EnergyComponentsCatalog *-- "0..*" CombinedHeatPower: chps
EnergyComponentsCatalog *-- "0..*" Manufacturer: manufacturers
EnergyComponent -up-> "1..1" Manufacturer: producedBy
----

The diagram models four types of technical components whose data shall be stored in the catalog, e.g. for parameterization of simulation models later: _Boiler_, _CombinedHeatPower_, _SolarPanel_, and _Inverter_.

The catalog itself is represented by class _EnergyComponentsCatalog_.
Unlike dozens, hundreds, or even thousands of objects to be cataloged -- Boilers, Inverters etc. -- there will be just exactly *one* catalog object in the data representing the catalog itself.
Its "singularity" is not visible in the class diagram, but an _Ecore_ convention requires that all objects must form a composition hierarchy with only one root object.

.Composition
If, in the domain, one object is composed of others, this is expressed by a special kind of association called _composition_.
Compositions are depicted as a link with a diamond shape attached to the containing object. In the _Boiler_ case said link translates to: The _EnergyComponentsCatalog_ contains -- or is composed of -- zero or more (`0..*`) boiler objects stored in a list named `boilers`.

[IMPORTANT]
====
Note that class names -- despite the fact that they model a set of similar objects -- are always written in _singular_!
Names for list-like associations and attributes usually are written in plural form.
====

.Inheritance
Besides composition of *objects*, the model above shows another, completely different, kind of hierarchy: the inheritance hierarchy between *classes*.
Whenever classes of objects share the same attributes or associations, we don't like to repeat ourselves by adding that attribute or relation to all classes again and again.
Instead, we add a _super class_ to define common attributes and associations and connect it to _sub classes_ that will automatically _inherit_ all the features of their super class.

In our example above, common to all four energy components are attributes `modelName` and `revisionYear`, thus these are modeled by class `EnergyComponent` that is directly or indirectly a super class of _Boiler_, _CombinedHeatPower_, _SolarPanel_, and _Inverter_.
Similar, _Boiler_ and _CombinedHeatPower_ share attribute `installedThermalPower` factored out by class _ChemicalDevice_.
_SolarPanel_ and _Inverter_ share attribute `nominalPower` modeled in abstract class _ElectricalDevice_.

.Associations
You probably noticed a fifth type of objects contained in the catalog, namely `Manufacturer` objects stored in list `manufactureres`.
How come? Ok, here is the story:

.Domain Expert Meets Developer
****
_Exp_: "`I'd like to store a component's manufacturer. Shall I add a String attribute `manufacturerName` to all classes like _Boiler_, _Inverter_ and so on to store the manufacturer's name?`"

_Dev_ shudders: "`Well, what do you mean by "... and so on"?`"

_Exp_: "`Basically, I mean all energy components.`"

_Dev_: "`Fine. We already have a class representing all those energy components, brilliantly named _EnergyComponent_. Thus, we can define `manfacturerName` there, following one of Developer's holy principles: "_DRY_ -- Don't repeat yourself!"
By the way: Is the name all you want to know about manufacturers?`"

_Exp_: "`Mhm, maybe we need to know if they are still in business ...`"

_Dev_: "`... or even since when they were out of business, if at all ...`"

_Exp_: "`... and the country or region they are active.`"

_Dev_: "`Ok, so it's not just the name -- we need a class `Manufacturer` to model all these information.`"

_Exp_ sighs.

_Dev_: "`Come on, its not that hard to add a class to our data model, isn't it?`"

_Exp_: "`Ok, but how can we express what components a manufacturer produces?`"

_Dev_: "`Wasn't it the other way around? I thought, you just wanted to know the manufacturer of a component?`"

_Exp_: "`What is the difference?`"

_Dev_: "`In data modeling, it is the difference between a uni-directional and a bi-directional association.`"

_Exp_: "`...?`"

_Dev_: "`Let's put it that way: The difference between a link with an arrow on one side or on both sides.`"

_Exp_: "`Ok. We don't need a list of components per manufacturer, but simply a reference from the component to its manufacturer.`"

_Dev_: "`Fine, then in Ecore please create a simple reference from class `EnergyComponent` to class `Manufacturer`, maybe named `producedBy`.`"

_Exp_: "`I will try this and get back to you.`"

_Dev_: "`Fine ... good meeting.`"
****

Observe in our data model, reference `producedBy` points _from_ `EnergyComponent` _to_ `Manufacturer` making it uni-directional reference.
One can simply query the manufacturer of a product, but not so the other way around.
With a bi-directional reference both queries would be available.

Observe also the annotations `0..*` and `1..1` near class `Manufacturer`.
These are _multiplicities_ of associations: An `EnergyComponentsCatalog` contains zero, one, or many objects of class `Manufacturer` and an `EnergyComponent` must reference exactly one manufacturer -- not less, not more.

[.float-group]
--
.Ecore Relations
image::EcoreRelations.gif[EcoreRelations, 200, float="right", role="thumb"]

To recapitulate: Our example parameter catalog already exhibits all four types of relations provided by Ecore.
You find these in the Ecore editor's palette shown here.
To create a relation between a sub class and a super class use tool `SuperType`.
Use the other tools to create an association between classes, may it be a simple (uni-directional) reference, a bi-directional reference, or a composition.
--

.Attributes and Enumerations

Obviously, attributes are central in data modeling.
Create one by dragging it from the palette onto our one and only class so far: `EnergyComponentsCatalog`.
The class symbol will turn red to indicate an error.
Hover with the mouse pointer over the new attribute and a tooltip with a more or less helpful error message will appear.
Current error is caused by that no data type was set for the new attribute.
Data types for attributes can be integer or floating point numbers, strings, dates, booleans, and more.
To get rid of the error:

. If not already selected, select new attribute by clicking at it in the editor.
. In view _Properties_ find `EType` and click button `...` to see a quite long list of available data types.
. Choose `EString [java.lang:String]` from the list and the error is gone.

[.float-group]
--
.Class with Attribute
image::EcoreClassWithAttribute.png[EcoreClassWithAttribute, 200, float="right", role="thumb"]

Change the attribute's name to `author` and the class should look like shown here.

Most data types to choose from begin with letter *E* like in **E**core.
These are just Ecore enabled variants of the respective Java types, thus, choose EInt for an int, EFloat for a 32 bit floating point number, EDouble for a 64 bit one, and so on.

Ecore allows to introduce new data types.
We employ this feature later to enable data models with physical units and quantities.  
--

There exists one other means to define the values an attribute can take, namely enumerations of distinct literals. Take _Monday_, _Tuesday_, _Wednesday_, ... as a typical example for representing weekdays.
In our example data model you'll find one _Enumeration_ named `BoilerType` with values `LowTemperature` and `Condensing`.

.Homework

The next section deals with generation of Java code from data models. To have more to play with, please implement our example model in Ecore now.

[.float-group]
--
.Abstract Class
image::EcoreClassifier.png[EcoreClassifier, 200, float="right", role="thumb"]

To do this, there is one more thing to know about classes: the difference between ordinary classes and abstract classes.
'Ordinary class' doesn't sound nice, therefore, classes that are not abstract are called _concrete_ classes.
Our example diagram depicts abstract classes with letter *A* while concrete classes are labeled with *C*. You add abstract classes to a model with a special palette tool shown here.

The thing is: Objects can be created for concrete classes only!

In our example, it makes no sense to create an object from class _EnergyComponent_, because there is not such a thing like an energy component _per se_.
Therefore, this class is _abstract_.
It is true that an inverter _is_ an energy component, thus inheriting all its features, but it was _created_ as _Inverter_, not as _EnergyComponent_.

Super classes will be abstract most of the time.
So my advice is: Model a super class as abstract class unless you convince yourself that there exist real objects in the domain that belong to the super class but, at the same time, do not belong to any of its sub classes.
In the Ecore editor properties view, you can specify if a class is abstract or not, simply by toggling check box `Abstract`.
--

Two more tips and you are ready to rock and roll! -- At least with your homework.

[TIP]
====
An exhaustive user manual for Ecore diagram editor is available. Execute `Help -> Welcome` and follow link `Learn how to use the diagram editor`.
====

[TIP]
====
If Ecore models get bigger, you may find it more convenient to work with a form based UI instead of, or in addition to, the diagram editor.
Open this kind of editor via command `Open With -> Ecore Editor` from the context menu over entry `democatalog.ecore` in the _Model Explorer_ view.
Note that Eclipse synchronizes different editors of the same content automatically.
====


=== Generation of Java Code from Data Model 

By now, your Ecore model should look like this:

[[fig-example-model]]
.Example Model (Homework)
image::Homework.png[Homework, role="thumb"]

Let us bring the model to life, that is, generate code from it that creates, reads, updates, and deletes concrete data objects of modeled classes in computers.
I would like to tell you that this is done with just one click but, actually, you need two or three:

. Make sure all files are saved (`File -> Save All`)
. Execute `Generate -> Model Code` from the context menu of Ecore editor `democatalog`
. Execute `Generate -> Edit Code` from the same context menu

[WARNING]
====
Please do *not* execute `Generate -> All` or `Generate -> Editor Code`.

image::GenerateMenu.png[GeneratedClasses, 260, role="thumb"]

This would create code for a simple user interface, but we use more advanced EMF Forms for that later.
If, by mistake, project `org.example.democatalog.editor` was created, just delete it from _Model Explorer_ and do not forget to check `Delete project contents on disk` in confirmation dialog.

====

[.float-group]
--
.Generated Classes
image::GeneratedClasses.png[GeneratedClasses, 260, float="right", role="thumb"]

`Generate -> Model Code` creates classes that represent the modeled data in code. These classes are located in three packages under directory `src-gen` in `org.example.democatalog`.

`Generate -> Edit Code` creates a whole new Eclipse project named `org.example.democatalog.edit`, again with generated classes under directory `src-gen`.

You may have a look at some Java classes for curiosity by double clicking at them in _Model Explorer_. There is no point in trying to understand the code in detail, but observe token `@generated` present in the comments of all classes, fields and methods. Classes, fields and methods marked with this token are (re)generated whenever above commands are executed.

Sometimes it maybe required to manually adapt generated code -- after all our concern is "low code", not "no code" development. In that case, we will replace `@generated` by `@generated NOT` to prevent code regeneration.

After code generation, you may have noticed some warnings showed up in view _Problems_.

.Warnings
image::Warnings.gif[Warnings, 500, role="thumb"]

In general, it is highly recommended to resolve warnings, and errors of course, but we will make an exception from the rule, since the warnings are uncritical and would reappear each time code is regenerated.
--


=== Generation and Tweaking of User Interface

In this section you will learn how to generate and tweak a CRUD user interface based on Ecore data model and Java classes created for our demo parameters catalog above. Topics described here are discussed in more detail in tutorial https://eclipsesource.com/blogs/tutorials/getting-started-with-EMF-Forms/[Getting started with EMF Forms].
To find out what user interface controls and layouts are provided by this framework have a look at https://eclipsesource.com/blogs/tutorials/emf-forms-view-model-elements/[EMF Forms – View Model Elements]. _EMF Forms_ is already part of package _Eclipse Modeling Tools_, so we can create a third Eclipse project/plugin that implements a user interface for editing catalog data without further ado:

. In the _Model Explorer_ execute `EMF Forms -> Create View Model Project` from context menu over `democatalog.ecore`
. Leave project name `org.example.democatalog.viewmodel` as is but uncheck `Use default location` -- as we always do -- and browse to the directory containing `org.example.democatalog`
. Click `Next >` and select `EnergyComponentsCatalog` as data element we want to create a user interface for
. Leave `Fill view model with default layout` checked and click `Finish`.

According to these inputs a new project is created with file `EnergyComponentsCatalog.view` under directory `viewmodels`.
This file opens automatically in a special _View Editor_.

.New View Model
image::ViewModel.png[ViewModel1, role="thumb"]

Like the *data* of our catalog are modeled as Ecore file using a dedicated graphical editor, so will our catalog’s *user interface* be modeled in `.view` files, again using a special editor.

Since we opted for `Fill view model with default layout` the catalog's UI is filled initially with default controls for all data items assigned to Ecore type `EnergyComponentsCatalog` like a string control for `author` or list controls for `boilers`, `chps`, and so on.

See red arrow in the above screen-shot?
It points to a button that opens a functional preview of the modeled user interface.

.User Interface Preview
image::ViewEditorPreview.png[ViewModel1, 500, role="thumb"]

[TIP]
====
Double click on tab _EMF Forms Preview_ to enlarge view for better handling -- double click again to get back.

Enable auto refresh mode image:ViewModelAutomaticRefresh.gif[ViewModelAutomaticRefresh, 40] to let each change in the view model instantly be reflected in the preview.

Given your screen is big enough, you may want to dock-out the preview by dragging tab _EMF Forms Preview_ out of Eclipse's main window.
Seeing editor and preview side by side is a great way to explore the possibilities of view models. 
====

Red input field and exclamation mark in the preview signal missing or inconsistent data.
Ecore data model specifies attribute `author` with a lower bound of one, meaning it is a mandatory attribute.
As soon as an author's name is provided, the error indication disappears.
This is what _functional_ preview means.
You can even create new boilers or other objects in lists provided, with all forms created "automagically" with respect to our underlying Ecore data model.

Of course, such automatic approach has its limits.
In our case, a long list of lists is not very user-friendly, because one has to scroll up and down to find a specific list.
Also, no specific object data are shown in the list and data can only be edited in a pop-up form (no inline editing).

How should a better UI look and feel like?

If there are many lists (types) of entities -- the normal case for parameter catalogs -- users should select what list they want to work with by selecting it from a list or tree view that is always visible, the _master view_.
Once a type is selected in the master view, a table with all objects of this list/type shall appear sidelong in a _detail view_, ready for editing.

In _EMF Forms_ master-detail-views can be modeled either with _Categorization_ or _Tree Master Detail_ UI components.
The latter not only allows to edit information displayed in the detail view, but also the tree of elements in the master view.
Opposed to that, a _Categorization_ presents a fixed hierarchy of elements to choose from.
This is exactly what we need as there are only a fixed number of types of objects to be edited in a parameters catalog.


==== Adding Tables to the UI
 
[.float-group]
--
.Delete default list controls
image::ViewModelDeleteControls.gif[ViewModelDeleteControls, 300, float="right", role="thumb"]

But first, we replace the default controls for lists of boilers, chps, and so on by tables. As shown here, select all list controls in the view model and execute `Delete` from context menu. Refresh _View Editor Preview_ to verify that only field `Author*` is left.
--

[.float-group]
--
.Create Table Control
image::ViewModelCreateTable.gif[ViewModelCreateTable, 300, float="right", role="thumb"]

Next, create a table that shall display all boilers in a catalog:
Select `EnergyComponentsCatalog`, activate context menu and choose `TableControl` from the list of available UI elements.
(EnergyComponentsCatalog represents the root view of the UI and, as such, accepts quite a lot of different UI components as child components.)

Entry `TableControl` was inserted into the list of interface elements below `Control author`.
Checking updated preview reveals no table but a message basically saying that a reference to the domain model is missing, in other words: _EMF Forms_ does not know yet what data to present in table.
Click on entry `TableControl` to see its details.
A red exclamation mark indicates the missing `Domain Model Reference*`.
Click on image:ButtonLinkPlus.gif[ButtonLinkPlus, 40] and be ready to chase a sequence of dialogs:
--

. Click on another image:ButtonLinkPlus.gif[ButtonLinkPlus, 40] in dialog `Configure TableDomainModelReference`

. In wizard `New Reference Element` select `model -> FeaturePathDomainModelReference` and click `Next >`

. Click `Link Domain Model EFeature` and in appearing pop-up list choose reference to list of objects you want to edit in the table, e.g. `boilers`; confirm with `OK` safely ignoring warning about missing `PropertyDescriptor`.

. `Finish` wizard `New Reference Element`

. `Finish` dialog `Configure TableDomainModelReference`.

This was some work, but as reward we get a fully specified table control in _View Editor_ that "translates" into a preview where we can create, read, update, and delete boilers.

.Table for Boilers
image::ViewModelWithTable.gif[ViewModelWithTable.gif, role="thumb"]

Moreover, clicking at a table header sorts all objects in it (rows) according to the values in this column. 
Column widths can adapted, too.

[.float-group]
--
.Modify Table Control
image::ViewModelTweakTable.gif[ViewModelTweakTable, 300, float="right", role="thumb"]

Table UIs can be tweaked in many ways, e.g. selection and sequence of columns can be declared via list `Column Domain Model References`. To fill this list with defaults, execute `Generate Columns` from table control's context menu. Reorder them as you like or delete columns that are not important to the user.

Notice here an important overall feature of _EMF Forms_: If something is left unspecified, be it the view model for an Ecore object type or the specification of table columns, _EMF Forms_ will always find a default solution! Applied to columns specification this means we get default columns automatically back in the moment the last column is removed from list `Column Domain Model References`.

If explicit column specifications are present further configurations can be added to a table control from its context menu, e.g. initial column widths or read-only status of columns. See https://eclipsesource.com/de/blogs/2018/01/31/emf-forms-1-15-0-feature-enhanced-table-renderer/[here] for details.
--

By default only attributes are displayed and directly editable in tables while references to other objects -- in our case the reference to a manufacturer -- are not.

[.float-group]
--
.Default  Panel for Boilers
image::ViewModelWithPanel.gif[ViewModelWithPanel, 300, float="right", role="thumb"]

To get the default (_sic!_) editing panel for an selected table row, in _View Editor_ just set `Detail Editing*` from `None` to `WithPanel`, *press _Tab_*, and save. For boilers, _EMF Forms_ will create the editing panel shown here. Regardless wether users edit data in the panel or directly in the table -- both will stay in sync any time.
--

[WARNING]
====
_View editor_ exhibits an irritating behavior: With preview auto-refresh turned on, any change in the details view is reflected instantly in the preview, even without saving the form or leaving the edited field.

On the other hand, *saving* an updated view editor only takes into account edited fields after they have lost focus, e.g. by pressing _Tab_ key or clicking with the mouse into another field.
So, saving a form before the focus has shifted from the last edited field won't honor this edit, that is you won't necessarily get what you see.
====

One last thing: Enter `boilers` as name for the table control so we can distinguish it from the other four table controls to come.

Yes! ... Please repeat above procedure to create table controls for chps, solar panels, inverters and manufacturers, too. I did this in about 3 minutes. ;-)


==== Master-Detail View with Categories

In last section we improved our catalog's UI by replacing simple object lists by tables that can be sorted, customized and edited inline as well as in an associated panel.
Alas, instead a list of lists we have got an even bigger list of tables.

High time to introduce a master-detail view that presents categories of object types in a master view and, after one is selected, the according object table in the detail view.

[.float-group]
--
.Category Tree
image::ViewModelCatgorization1.gif[ViewModelCatgorization1, 180, float="right", role="thumb"]

Add a _Categorization_ view to the list of UI elements in _View Editor_ by selecting `EnergyComponentsCatalog` and choose `Categorization` from its contect menu.

Now add two `Composite Category` elements and one `Leaf Category` to `Categorization` from according context menu. This gives us three top level entries in the hierarchy.

In the same way add two `Leaf Category` elements to each `Composite Category` resulting in the hierarchy depicted here.
--

[.float-group]
--
.Completed View Model
image::ViewModelCatgorization2.gif[ViewModelCatgorization2, 260, float="right", role="thumb"]

This screen shot shows the view model of our UI when finished. To get there:

. Select UI element `Categorization` and rename it to `Categories`

. Rename composite and leaf categories as depicted here

. Drag all table controls one by one into the suited leaf category

. Confirm master-detail view works as expected in the preview.

--

[IMPORTANT]
====
The UI hierarchy to access tables for entity types is independent, and usually will differ, from aggregation and inheritance hierarchies present in Ecore data model (compare fig. <<fig-example-model, Example Model>>).
====

Note that _EMF Forms Preview_ provides these buttons image:ViewModelPersistence.gif[PreviewPersistanceButtons, 68] to clear, load and store edited data.
In fact, this feature gives us a fully functional prototype.
At least during refinement of model and UI, data sets can be created, edited, and tested for usability without the need to built a full blown, deployable application -- see parts _Accessing and Using Parameter Catalogs_ and _Build (Parameter Catalog) Applications with Eclipse Tycho_ below.

Be aware that in some cases the view model must adapt to changes in data model, e.g. a new leaf category and table component must be created for a new catalog object type.
Other changes are automatically reflected in the generated UI, at least for default forms and default table columns.
To our convenience, view model specifications incompatible with data model are indicated by error badges in the _View Editor_.

Changes in data model also can make existing XML data incompatible. There are tools for data migration, but for now, recreation of test data or manual editing of XML file is the way to go.


==== Summary

What have we achieved so far?

We created a graphical Ecore data model with a catalog class and five classes/types of objects therein.
Classes have been defined by name, attributes, and relations between them, often with cardinalities.
Whenever classes shared some attributes or references we factored these out into super classes.
An enumeration introduced a new attribute type as a set of named values.

From this data model, we issued commands to create Java code for representing the data in memory as well as to store and retrieve them on and from disk. Methods to create, read, update and delete data objects (CRUD) were generated, too.

Lastly, we thought about a good user interface for this data and used _EMF Forms_ to model it resulting in a full functional prototype.


=== Bonus: Solutions for Specific Modeling Problems


==== Add Units to the Mix

*TBD*

As mentioned earlier, parameter catalogs for simulations should be able to represent quantities, not just bare integer and real numbers.

using Indrya, the reference implementation for Units of Measurement in Java (JSR 385)

To this end, the author has created two Eclipse plug-in projects providing this feature to be used by Ecore and EMF Forms.

Third-party libraries like Indrya, usually, are not distributed as plug-ins, but _Tycho_ can wrap them automatically as OSGi plug-ins that can added directly to our application.

Another plug-in, created by the author connects the Ecore and Indrya. We will compile it from source code, simply by importing the projects.

. Copy to file system ...
. Import project but *not* copying it in the workspace (just linking)


==== Represent Functions in a Parameter Catalog

*TBD*

for creating custom UI labels:

* `ExponentialFunctionItemProvider.java`
* `LinearFunctionItemProvider.java`
* `TableFunctionItemProvider.java`

Custom code marked with `@generated NOT` in `de.hftstuttgart.energycomponents.provider` in project `de.hftstuttgart.energycomponents.edit`

==== How to Model Derived References and Attributes

*TBD*

We haven't used derived references or attributes by now. But if one has to implement some by providing a getter, it is necessary to return an unmodifiable list like BasicEList.UnmodifiableEList or EcoreUtil.unmodifiableList(...) instead of EList as described here: https://www.ntnu.no/wiki/plugins/servlet/mobile?contentId=112269388#content/view/112269388 .

