Let's assume an operator is running the Alarm Table shown in Figure 2.1, “CSS Alarm Table”. This application displays current alarms, and the operator notices a power supply voltage fault that needs further investigation. The alarm table indicates that this fault was reported by the Process Variable MEBT_CHOP:PS_2:V. Using separate tools, the operator could start a strip charting application, and enter the PV name into that other tool to review how the voltage changed over time. There may also be a way to copy and paste the PV name from the alarm table to the strip chart, but in any case the operator will first have to start the strip chart application.

Enter CSS context menus: When right-clicking on the alarm under investigation in the alarm table, a context menu opens up, see Figure 2.2, “Context Menu”. It lists entries specific to this alarm, for example it allows the operator to acknowledge the alarm. In addition, there are links to other CSS tools, including the Data Browser. The Data Browser is a strip-charting tool for CSS. Selecting this Data Browser entry will open a new Data Browser plot and add the PV associated with the alarm to the Data Browser. With CSS, the task of opening another tool, then copying and pasting a PV name or even manually entering it has been reduced to a mouse click in the context menu!

In the Data Browser, the operator can now inspect the behavior of the PV over time. She might notice that the power supply voltage indeed dropped down, causing the alarm. In addition, she can see that the same voltage drop has occurred before, about one day ago. The operator can add annotations to the plot to indicate the time of the current as well as previous voltage drop.

Eventually, the operator handles the alarm: Whatever caused the voltage to drop is understood and fixed. Especially when a similar event has happened before, as a day ago in this example, it makes sense to add a note to the electronic logbook, or to send an email to the engineer who maintains the power supply. If a site that uses CSS has an electronic logbook system (ELog), for example with a web interface, one could save a screen-shot of the Data Browser plot to a file, then go to a web browser, log into the ELog, describe the problem, attach the Data Browser screen-shot, submit the entry. With CSS, this can again be integrated: The context menu of the Data Browser plot directly offers a Logbook... link, see Figure 2.4, “Electronic Logbook Submission”. When activated, a basic text entry with attached Data Browser screen-shot is prepared. The operator can enter the text, provide the user name and password that she uses in the ELog system, and submit the entry right from within CSS.

In summary, the whole work flow for handling an alarm that would otherwise require an operator to start separate stand-alone applications can be integrated within CSS:

There is no need to copy/paste PV names, there is no need to save a screen-shot as an image file, remember the location of that file, then open another application to attach the file to an ELog entry.

The functionality of Control System Studio (CSS) that we described in the previous example is implemented in Java, using the Eclipse software framework, specifically the Rich Client Platform (RCP).

The Java programming language and runtime environment allows the creation of software that can be used on several operating systems like Microsoft Windows, Linux and Apple Mac OS X. The same CSS application code can thus run in the control room as well as on office computers. While the Java runtime might in certain cases be slower than a program that was specifically created for a certain operating system in a language like C++, the speed is usually "good enough", and there are more advantages:

It is hard to imagine that a program suite as complex as CSS could have been implemented without Java.

As Java code becomes more complex, it can be split into several library files called Java Archives or 'JAR' files. The Java runtime can dynamically load and unload these libraries. Through introspection it is possible to locate features in such JAR files. For example, one can create a Java program that communicates with a control system, where the specific network protocol implementation is in a JAR file. While developing or later extending the software, a test JAR file is used to simulate a control system. For the operational setup, a site-specific JAR file connects the software to the actual control system. The same program can be used at different sites because the site-specific portion of the code is "plug-able".

While Java supports such dynamic binding, it does not enforce a standard way to do this. The Eclipse software framework provides three key elements:

An Eclipse Product combines selected plugins with configurations files and a Launcher. Traditionally, Java products require a Unix shell script or a Windows batch file to set certain environment variables, configure the Java CLASSPATH, and finally invoke the Java runtime. Eclipse provides each product with a Launcher, which is an application native to the operating system. The Launcher can display a “Splash” screen, locate the Java Runtime, configure it, and finally start the product. To the end user, an Eclipse product thus looks just like any other application that is native to the operating system. CSS has icon and shows up as CSS in the task bar or process list, while traditional Java programs often appeared as shell scripts. While almost all the CSS and Eclipse Java code is fully portable across operating systems, this Launcher is specific to an operating system.

Another part that is operating system specific is the Eclipse Standard Window Toolkit (SWT). Java itself provides the Abstract Window Toolkit (AWT) to generate user interface code. At least in the past, AWT had an appearance that clearly differed from the native user interface of the operating system on which a Java application ran. The Eclipse community developed SWT, which always uses the native user interface elements of an operating system. For example, SWT on Mac OS uses Cocoa widgets, while SWT on Linux uses GTK widgets. The Eclipse and CSS code mostly uses SWT in a transparent way, but when building a product for a certain operating system, Eclipse includes the SWT plugins that are specific to that operating system.

Control System Studio is an Eclipse RCP product, i.e. fundamentally just a collection of Eclipse Plug-ins. In CSS, what could otherwise be a stand-alone control system application turns into a Plug-in, for example:

In principle, these could each be separate programs. Users would individually start and stop them as needed. In CSS, they become Plug-ins of the CSS product. Users run CSS, then start Probe or the Data Browser from within CSS. Just as a site integrator might choose which individual programs to install in the control room, she can add Plug-ins to CSS or remove them from CSS based on local requirements.

As a side note, there still are individual applications: The Alarm Server, the Archive Engine are examples for stand-alone RCP applications that use essential CSS library code, but they are nevertheless executed as individual application instances. In the following we are concentrating on the CSS product that end users see in the control room or on their office computers, where they typically run one instance of CSS and inside that includes Probe, EPICS PV Tree, Data Browser and other CSS tools.

So what are the advantages of a combined Eclipse/CSS product over individual Java applications? For one, the online help and preference settings of Probe, EPICS PV Tree, Data Browser and other CSS tools are integrated. As shown in Figure 2.5, “CSS Preference Panel”, one preference panel, opened from the menu bar under Edit/Preferences, provides access to all settings: Alarm system connectivity used by the Alarm Table, Data Browser settings can be found under the Trends section, and also generic control system settings like the EPICS connection parameters under CSS Core.

If the alarm plugins were removed from the CSS product shown in Figure 2.5, “CSS Preference Panel”, the related settings would simply disappear from the preference panel. Likewise, when additional plugins are added to the CSS product, their preference settings will appear in the panel. With standalone, pre-Eclipse control system applications, the preference settings were provided via environment variables or configuration files. Details tended to differ for each application. With CSS, the same Eclipse preference system applies to all application plugins. More in this in Chapter 6, Hierarchical Preferences.

CSS similarly benefits from the Eclipse/RCP online help system. Whenever CSS plugins include online help pages, these pages become part of the online help system, with global seach support.

What distinguishes CSS plugins from generic RCP plugins is the use of control system specific extension points. CSS defines extension points for providing live or archived data, to submit text and images to an electronic logbook. CSS application plugins can be implemented as users of these extension points. Combined with site-specific implementations of these extension points, a product is created that will for example get live data from EPICS Channel Access, archived data from a MySQL database, and send submissions to an electronic logbook that keeps its data in an Oracle database.

CSS furthermore defines control system specific classes like a Process Variable. Combined with an RCP mechanism called Object Contributions, this results in the seamless workflow between applications described in the section called “Example Use Case”: In the Alarm Table, each line that displays alarm information also “is” a process variable. The Data Browser is a tool that understands process variables. It registers with Eclipse as an Object Contribution for context menues whenever a process variable is selected. The Alarm Table code is not at all aware of the Data Browser, it simply displays a context menu with alarm related entries like “acknowledge”. Eclipse detects that the currently selected alarm table row also represents a process variable. Eclipse adds the Data Browser entry to the context menu, and when the user invokes that entry, Eclipse will start the Data Browser with the process variable name.

Based on the Object Contribution mechanism, applications that deal with PV names can exchange them without having any knowledge of each other; they remain seperate plugins, possibly implemented by different people. When a new PV-aware plugin is added to a CSS product, it will automatically appear in context menues of all other plugins that provide PVs.

Another feature that Eclipse/RCP offers are online updates: The CSS product can be build such that users download it onto their office computer. When the local CSS administrator publishes software updates to a site-specific update site, CSS will detect this on the next startup and prompt the user to update to the latest version. Similarly, optional CSS components that only some user need can be placed on a site-specific update site such that these users add them to their CSS product as needed.