Package Management

Overview of Basic Modelica Package Management Concepts

The Modelica language promotes the orderly reuse of component models by means of packages that contain structured libraries of reusable models. The most prominent example is the Modelica Standard Library (MSL), that contains basic models covering many fields of engineering. Other libraries, both open-source and commercial, are available to cover specific applications domains.

When you start a simulation project using Modelica, it is common practice to collect all related system models in a project-specific package that you develop. The models in this package are often instantiated (e.g. by drag-and-drop in OMEdit) from released libraries, which are read-only for your project. This establishes a dependency between your project package and a certain version of a read-only package (or library), which is the one you have loaded in OMEdit and that you drag-and-drop components from.

This dependency is automatically marked in your package by adding a uses annotation at the top level. For example, if you drag and drop components from MSL 4.0.0 into models of your package, the annotation(uses(Modelica(version="4.0.0"))); will be added automatically to it. This information allows OpenModelica to automatically load all the libraries that are required to compile the models in your own package next time you (or someone else, possibly on a different computer) loads your package, provided they are installed in places on the computer's file system where OpenModelica can find them.

The default place where OpenModelica looks for packages is the so-called MODELICAPATH. You can check where it is by typing getModelicaPath() in the Interactive Environment (Tools | OpenModelica Compiler CLI in OMEdit). Installed read-only libraries are placed by default in the MODELICAPATH.

When a new version of certain package comes out, conversion annotations in it declare whether your models using a certain older version of it can be used as they are with the new one, which is then 100% backwards-compatible, or whether they need to be upgraded by running a conversion script, provided with the new version of the package. The former case is declared explicitly by a conversion(noneFromVersion) annotation. For example, a conversion(noneFromVersion="3.0.0") annotation in version 3.1.0 of a certain package means that all packages using version 3.0.0 can use 3.1.0 without any change. Of course it is preferrable to use a newer, backwards-compatible version, as it contains bugfixes and possibly new features.

Hence, if you install a new version of a library which is 100% backwards-compatible with the previous ones, all your models that used the old one will automatically load and use the new one, without the need of any further action.

If the new version is not backwards-compatible, instead, you will need to create a new version of your library that uses it, by running the provided conversion scripts.

OpenModelica has a package manager that can be used to install and update libraries on your computer, and is able to run conversion scripts. Keep in mind there are three stages in package usage: available packages are indexed on the OSMC servers and can be downloaded from public repositories; installed packages are stored in the MODELICAPATH of your computer; loaded packages are loaded in memory in an active OMC session, either via the Interactive Environment, or via the OMEdit GUI, where they are shown in the Libraries Browser. When you load a package, OpenModelica tries to load the best possible installed versions of all the dependencies declared in the uses annotation.

The Package Manager

The Open Source Modelica Consortium (OSMC) maintains a collection of publicly available, open-source Modelica libraries on its servers, see https://github.com/OpenModelica/OMPackageManager. These libraries are routinely tested with past released versions of OpenModelica, as well as with the current development version on the master branch, see the overview report. Based on the testing results and on information gathered from the library developers, these packages are classified in terms of level of support in OpenModelica. Backwards-compatibility information is also collected from the conversion annotations.

The OpenModelica Package Manager relies on this information to install the best versions of the library dependencies of your own, locally developed Modelica packages and models. It can be run both from the OMEdit GUI and from the command-line interactive environment. The libraries and their index.json index file with all the library metadata are installed in the ~/.openmodelica/libraries directory under Linux and in the %AppData%\.openmodelica\libraries directory on Windows. Note that these directories are user-specific, so if there are multiple users on the same computer, each of them will install and manage his/her own set of libraries independently from the others.

The Package Manager may install multiple builds of the same library version in your own package manager directory, if they are indexed on the OSMC servers. When this happens, they are distinguished among each other by means of semver-style pre- or post-release metadata in the top directory name on the file system. Post-release builds are denoted by a plus sign (e.g. 2.0.0+build.02) and have higher priority over the corresponding plain release (e.g. 2.0.0), while pre-release builds are denoted by a minus sign (e.g. 2.0.0-dev.30) and have a lower priority.

When loading a certain version of a library, unless a specific build is explicitly referenced, the one with higher precedence will always be loaded. For example, if the versions 2.0.0-beta.01, 2.0.0, and 2.0.0+build.01 are installed, the latter is loaded by libraries with uses annotation requiring version 2.0.0. Unless, of course, there are later backwards-compatible versions installed, e.g., 2.0.1, in which case the one with the highest release number and priority is installed.

In any case, semver version semantics is only used to order the releases, while backwards-compatibility is determined exclusively on the basis of noneFromVersion annotations.

When installing OpenModelica, a cached version of the latest versions of the Modelica Standard Library is included in the installation files. As soon as a user starts any OpenModelica tool (e.g., OMEdit, OMNotebook, OMShell, or direct command-line invocation of omc), if the user's .openmodelica directory is empty the Modelica Standard Library will be installed automatically using this cached version. This happens when using OpenModelica for the first time, or if the contents of the .openmodelica directory have been deleted to get rid of all installed libraries. This automatic installation needs no Internet connection, so it also works behind firewalls or in set-ups with limited available bandwidth. Therefore, the Modelica Standard Library is immediately available without the need of using the package manager explicitly. It is then possible to install and manage other libraries using the package manager, as explained previously.

Package Management in OMEdit

Installing a new library in OMEdit.

Running Conversion Scripts in OMEdit

Converting a library in OMEdit.

Automatically Loaded Packages in OMEdit

When you start OMEdit, some packages can be automatically loaded into the environment, and shown in the Libraries Browser. You can configure which ones are loaded from the Tools|Options|Libraries menu.

Please note that automatically loaded libraries may be in conflict with the dependencies of packages that you may later load from the File menu. For example, if you automatically load Modelica 4.0.0, and then load a library XYZ that still uses MSL 3.2.3, you get a conflict, because Modelica 4.0.0 is not backwards-compatible with Modelica 3.2.3, so XYZ cannot be used.

In this case you have two options:

  • Cancel Operation: this means XYZ is not actually loaded, and all previously loaded libraries remain in place.

  • Unload all and Reload XYZ: in this case, all previously loaded libraries, that may generate conflicts, are unloaded first; then XYZ is loaded, and finally the right versions of the libraries XYZ uses, as declared in its uses annotation, will be loaded automatically.

If you are normally working with only one version of the Modelica standard library, you can set it to be automatically loaded from the Tools|Options|Libraries menu; in case you need to work with a library that uses a previous, non-backwards compatible version, the Unload all and Reload option comes handy. Otherwise, you can avoid loading the Modelica library automatically upon starting OMEdit, and let the right version of the Modelica library be loaded automatically when you open the library you want to work with. In this case, if you want to get the Modelica library into the Package Browser to start developing a new library, you can do so easily from the Welcome tab, by clicking on the System Libraries button and selecting the version that you want to load.

Manually Loading Packages

If you want to maintain full control over which library dependencies are loaded, you can use the File | Open Model/Library Files(s) menu command in OMEdit to open the libraries one by one from specific locations in your file system. Note, however, that whenever a library is loaded, its dependencies, that are declared in its uses annotation, will automatically be loaded. If you want to avoid that, you need to load the library dependencies in reverse order, so that the intended library dependencies are already loaded when you open the library that needs them.

If you are using the Interactive Environment, you can use the loadFile() command to load libraries from specific locations on the file system, also in reverse dependency order, unless you also set the optional uses = false input argument to disable the automatic loading of dependencies.

Using the Package Manager from the Interactive Environment

The Package Manager can also be used from the Interactive Environment command line shell. Here is a list of examples of relevant commands; please type them followed by getErrorString(), e.g., updatePackageIndex(); getErrorString(), in order to get additional information, notifications and error messages.

How the package index works

The package index is generated by OMPackageManager on an OSMC server, based on these settings. See its documentation to see how to add new packages to the index, change support level, and so on.

The index is generated by scanning git repositories on github. All tags and optionally some specific branches are scanned. The tag name is parsed as if it was a semantic version, with prerelease and metadata of the tag added to the version of Modelica packages in the repository. If the tag name is not a semantic version, it is sorted differently.

Packages are sorted as follows:

  • Support level: each package is given a level of support in the index

  • Semantic version: according to the semver specification, but build metadata is also considered (sorted the same way as pre-releases)

  • Non-semantic versions: alphabetically