BMI: Difference between revisions

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{{PageTitle| Basic Model Interface (BMI) }}


=   '''CSDMS Basic Modeling Interface (version 1.0)''' =
<div class=AutoScaleImage>[[ File:Bmi-logo-below-lowercase.png | 325 px | right ]]</div>
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* In order to simplify conversion of an existing model to a reusable, plug-and-play model component, CSDMS has developed a simple interface called the '''''Basic Model Interface''''' or '''BMI'''.  Recall that in this context an '''''interface''''' is a named set of functions with prescribed function names, argument types and return types.
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* By design, the BMI functions are straightforward to implement in any of the languages supported by CSDMS, which include C, C++, Fortran (all years), Java and Python.  Even though some of these languages are object-oriented and support user-defined types, the BMI functions use only simple (universal) data types.
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* Also by design, the BMI functions are '''''noninvasive'''''.  A BMI-compliant model is not required to use CSDMS data structures and does not make any calls to CSDMS components or tools.  BMI therefore introduces no dependencies into a model and the model can still be used in a "stand-alone" manner.
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* Any model that provides the BMI functions can be easily be converted to a CSDMS plug-and-play component with  a CSDMS '''''Component Model Interface''''' or '''CMI'''.  The BMI functions are called by the CMI, by the framework and by service components.  It is not necessary for a developer to learn anything about the CMI unless they're just curious.
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* Once a BMI-compliant model has been wrapped with the CMI interface to become a CSDMS component, it automatically gains many new capabilities.  This includes the ability to be coupled to other models even if their (1) programming language, (2) variable names, (3) variable units, (4) time-stepping scheme or (5) computational grid is different.  It also gains (1) the ability to write output variables to standardized NetCDF files, (2) a "tabbed-dialog" graphical user interface (GUI) (this requires a corresponding XML file) (3) a standardized HTML help page and (4) the ability to run within the CSDMS Modeling Tool (CMT).
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* The CMI wrapping does not have a significant impact on performance.  This is due to the use of [https://computation.llnl.gov/casc/components/#page=home '''Babel'''] for language interoperability and the fact that CSDMS components pass values '''''by reference''''' instead of '''''by copy''''' whenever possible.


<br/>
'''Version 2.0'''
<!-- ============================================= -->
== {{ Bar Heading| text=Fine-grained Control Functions}} ==
:
<syntaxhighlight lang=sidl>
void initialize (in string config_file)
void update (in double dt) //  Advance model variables by time interval, dt (dt=-1 means use model time step)
void finalize ()
void run_model (in string config_file) //  Do a complete model run. Not needed for CMI.
</syntaxhighlight>
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* These BMI functions are critical to plug-and-play modeling because they allow a calling component to bypass a model's own time loop.  They also provide the caller with fine-grained control over the model, similar to a TV remote control.


<br/>
Automobiles benefit from a standard interface--regardless of whether you drive a pickup truck or an electric two-seater,
<!-- ============================================= -->
you have an ignition, an accelerator, and steering wheel.
== {{ Bar Heading| text=Model Information Functions}} ==
Imagine spending weeks of study to switch from one type of automobile to another,
:
or from one brand to another.
<syntaxhighlight lang=sidl>
At CSDMS,
array<string> get_input_var_names()
we believe that numerical models, and the sub-components that make up these models, should offer a similar kind of standardization.
array<string> get_output_var_names()
To this end, we have developed the Basic Model Interface (BMI): a set of standard query and control functions that, when added to a model code, make that model both easier to learn and easier to couple with other software.
string get_attribute( in string att_name ) // (for model_name, mesh_type, time_step_type, etc.)
</syntaxhighlight>
:
* These BMI functions are called by the CSDMS framework in order to determine what input variables each model component needs and what output variables it can provide to other components.


* Note that "long variable name" and "long_var_name" refer to standardized variable names from the [[CSDMS_Standard_Names | '''CSDMS Standard Names''']].
BMI is an element of the [[Workbench|CSDMS Workbench]], an integrated system of software tools, technologies, and standards for building and coupling models.


* The '''''get_input_var_names()''''' function returns a string array of the model's input variable names as "long variable names".  Similarly, the '''''get_output_var_names()''''' function returns a string array of the models output variable names.
== Links ==


* The '''''get_attribute()''''' function is passed an attribute name from the following list:
* The latest [http://bmi.readthedocs.io/ BMI documentation], including the [https://bmi.readthedocs.io/en/latest/bmi.getting_started.html Getting Started Guide] and [https://bmi.readthedocs.io/en/latest/bmi.best_practices.html BMI Best Practices].
model_name
* The central BMI repository on [https://github.com/csdms/bmi GitHub]: Go here to contribute to BMI, ask a BMI-related question, or submit an issue.
author_name
* The BMI 2.0 language specifications for [https://github.com/csdms/bmi-c C], [https://github.com/csdms/bmi-cxx C++], [https://github.com/csdms/bmi-fortran Fortran], [https://github.com/csdms/bmi-java Java], and [https://github.com/csdms/bmi-python Python]. If you have a model in one of these supported languages, implement the corresponding spec to create a BMI.
mesh_type
* Sample implementations in [https://github.com/csdms/bmi-example-c C], [https://github.com/csdms/bmi-example-cxx C++], [https://github.com/csdms/bmi-example-fortran Fortran], [https://github.com/csdms/bmi-example-java Java], and [https://github.com/csdms/bmi-example-python Python]. These examples demonstrate how to implement a BMI for a simple model.
time_step_type
* The [http://www.sciencedirect.com/science/article/pii/S0098300412001252 Peckham et al. (2013) article] in ''Computers & Geosciences'' where the concept of BMI was proposed.
:and returns a corresponding string. For the "mesh_type" attribute, the allowed return values are:
* The [https://joss.theoj.org/papers/10.21105/joss.02317 Hutton et al. (2020) article] in ''Journal of Open Source Software'' describing BMI 2.0.
uniform, rectilinear, s_mesh and u_mesh
:as described below. For the "time_step_type" attribute, the allowed return values are:
fixed, adaptive, local


<br/>
== Citation ==
<!-- ============================================= -->
== {{ Bar Heading| text=Variable Information Functions}} ==
:
<syntaxhighlight lang=sidl>
string get_var_type( in string long_var_name ) // ( returns type_string, e.g. ‘double’)
string get_var_units( in string long_var_name ) // ( returns unit_string, e.g. ‘meters’ )
int get_var_rank( in string long_var_name ) // ( returns array rank or 0 for scalar)
string get_var_name( in string long_var_name ) // ( returns model’s internal, short name )
double get_time_step() // (returns the model’s current timestep;  adaptive or fixed.)
string get_time_units() // (returns unit string for model time, e.g. ‘seconds’, ‘years’)
double get_start_time()
double get_current_time()
double get_end_time()
</syntaxhighlight>


:
If you use BMI in your work, please cite:
* These BMI functions are called by the CSDMS framework to obtain information about a particular input or output variable.  Based on this information, the framework can apply type or unit conversion when necessary.


* Note that "long variable name" and "long_var_name" refer to standardized variable names from the [[CSDMS_Standard_Names | '''CSDMS Standard Names''']].
* Hutton, E.W.H., Piper, M.D., and Tucker, G.E., 2020. The Basic Model Interface 2.0: A standard interface for coupling numerical models in the geosciences. ''Journal of Open Source Software'', '''5(51)''', 2317, https://doi.org/10.21105/joss.02317.


 
* Peckham, S.D., Hutton, E.W., and Norris, B., 2013. A component-based approach to integrated modeling in the geosciences: The design of CSDMS. ''Computers & Geosciences'', '''53''', pp.3-12, http://dx.doi.org/10.1016/j.cageo.2012.04.002.
'''GET_VAR_TYPE''': Return data type of a variable as a string. Some possible values are given in the following table.
 
{|
! align=left width=250 | BMI datatype
! align=left width=150 | C datatype
|-
| BMI_CHAR
| <tt>char</tt>
|-
| BMI_UNSIGNED_CHAR
| <tt>unsigned char</tt>
|-
| BMI_INT
| <tt>signed int</tt>
|-
| BMI_LONG
| <tt>signed long int</tt>
|-
| BMI_UNSIGNED
| <tt>unsigned int</tt>
|-
| BMI_UNSIGNED_LONG
| <tt>unsigned long int</tt>
|-
| BMI_FLOAT
| <tt>float</tt>
|-
| BMI_DOUBLE
| <tt>double</tt>
|-
|}
 
<br/>
<!-- ============================================= -->
== {{ Bar Heading| text=Variable Getter and Setter Functions}} ==
:
<syntaxhighlight lang=sidl>
double get_0d_double( in string long_var_name )
array<double> get_1d_double( in string long_var_name  )
array<double,2> get_2d_double( in string long_var_name )
array<double> get_2d_double_at_indices( in string long_var_name, array<int> indices )
void set_0d_double( in string long_var_name, in double scalar )
void set_1d_double( in string long_var_name, in array<double> array)
void set_2d_double( in string long_var_name, in array<double,2> array)
void set_2d_double_at_indices( in string long_var_name, in array<int> indices, in array<double,2> array)
</syntaxhighlight>
 
<br/>
<!-- ============================================= -->
== {{ Bar Heading| text=Grid Information Functions}} ==
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* The BMI function call '''''get_attribute( "mesh_type" )''''' should return one of the following strings:
 
uniform      (for uniform rectilinear)
rectilinear  (for rectilinear)
s_mesh        (for structured mesh)
u_mesh        (for unstructured mesh)
 
* Each of these strings corresponds to a particular type of model grid or mesh. In order to provide a complete and standardized description of a model's grid, there is a different set of BMI functions that are required for each model "mesh_type" as described in this section.
 
* Note that an '''''orthogonal curvilinear''''' coordinate system is a special case of a "structured mesh".
 
* Note that "uniform rectilinear", "rectilinear" and "structured mesh" all have the topology of a two-dimensional array.
 
=== &nbsp; Uniform Rectilinear ===
 
[[Image:mesh_uniform_rectilinear.png|300px|wrap]]
<syntaxhighlight lang=sidl>
array<double, 1> get_grid_spacing (in string long_var_name)
array<double, 1> get_grid_lower_left_corner (in string long_var_name)
array<int, 1> get_grid_shape (in string long_var_name)
</syntaxhighlight>
 
=== &nbsp; Rectilinear ===
[[Image:mesh_rectilinear.png|300px|wrap]]
<syntaxhighlight lang=sidl>
array<double, 1> get_grid_x (in string long_var_name)
array<double, 1> get_grid_y (in string long_var_name)
array<double, 1> get_grid_z (in string long_var_name)
array<int, 1> get_grid_shape (in string long_var_name)
</syntaxhighlight>
 
=== &nbsp; Structured Mesh ===
[[Image:mesh_structured.png|300px|wrap]]
<syntaxhighlight lang=sidl>
array<double, 1> get_grid_x (in string long_var_name)
array<double, 1> get_grid_y (in string long_var_name)
array<int, 1> get_grid_shape (in string long_var_name)
</syntaxhighlight>
 
=== &nbsp; Unstructured Mesh ===
[[Image:mesh_unstructured.png|300px|wrap]]
<syntaxhighlight lang=sidl>
array<double, 1> get_grid_x (in string long_var_name)
array<double, 1> get_grid_y (in string long_var_name)
array<int, 1> get_grid_connectivity (in string long_var_name)
array<int, 1> get_grid_offset (in string long_var_name)
</syntaxhighlight>
 
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Latest revision as of 14:31, 3 January 2024

Basic Model Interface (BMI)
Bmi-logo-below-lowercase.png

Version 2.0

Automobiles benefit from a standard interface--regardless of whether you drive a pickup truck or an electric two-seater, you have an ignition, an accelerator, and steering wheel. Imagine spending weeks of study to switch from one type of automobile to another, or from one brand to another. At CSDMS, we believe that numerical models, and the sub-components that make up these models, should offer a similar kind of standardization. To this end, we have developed the Basic Model Interface (BMI): a set of standard query and control functions that, when added to a model code, make that model both easier to learn and easier to couple with other software.

BMI is an element of the CSDMS Workbench, an integrated system of software tools, technologies, and standards for building and coupling models.

Links

Citation

If you use BMI in your work, please cite:

  • Hutton, E.W.H., Piper, M.D., and Tucker, G.E., 2020. The Basic Model Interface 2.0: A standard interface for coupling numerical models in the geosciences. Journal of Open Source Software, 5(51), 2317, https://doi.org/10.21105/joss.02317.
  • Peckham, S.D., Hutton, E.W., and Norris, B., 2013. A component-based approach to integrated modeling in the geosciences: The design of CSDMS. Computers & Geosciences, 53, pp.3-12, http://dx.doi.org/10.1016/j.cageo.2012.04.002.
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