# Examples¶

## The data source¶

For this example we make a data source by fetching some data from Wikipedia. For some of the smaller countries it shows a nice table with average high and low temperatures per month and year. When we copy this data for some countries into an excel spreadsheet, we can use the XLSProvider to read this data into AIMMS. A screenshot of parts of our resulting data source is shown in the picture.

• Table names: If we look at the bottom we see that we have two worksheets with the names “Average High” and “Average Low”. These are the table names used in specifying the data map for DataLink. As we can see the table “Average High” is active, and it contains the average temperature value for each country per month.
• Column names: The top row in the picture contain the names of the columns. It starts with “Country” followed by the shortened names of months. These are the column names used in the mapping. Instead of talking about the columns in the spreadsheet way with letters ‘A’, ‘B’ ,etc., DataLink addresses each column by it’s name “Country”, “Jan”, “Feb”, etc. We can see that the values in column “Country” are strings (representing the countries), and that the month-columns all have floating point values (representing the temperature in Celsius).

## The AIMMS model¶

In AIMMS we declared identifiers and we want to read data from the data source above into these identifiers. Assume we have the following identifiers in our AIMMS model:

DeclarationSection Average_High_Declaration {
Set Countries {
Index: c;
}
Parameter January {
IndexDomain: c;
}
Parameter May {
IndexDomain: c;
}
}


In this declaration section we see that we have one set Countries with index c, and two parameters January and May that have index c as domain. It is clear from the data source what data has to be read into which identifier. The values from column “Country” should be read into set Countries and the columns “Jan” and “May” should be read into January and May.

We can now look at what DataLink has to do in order to read data from the source into the model. For each row in the data source it has to read in the value of the domain c (i.e. Iceland) and make sure that it exist in the AIMMS model. Then it can read in the value of the parameters (I.e for Jan 1.9), but it also has to tell that this value corresponds to domain c that was read in just before (Iceland). In AIMMS the columns are not independent and domain values have to be send to AIMMS multiple times. DataLink can speed this up by using some clever caching such that domain values only need to be send once.

## The data map¶

Now we have the data source and the identifiers in AIMMS, so we can define a data map that connects them. The data map itself is an identifier (string parameter) in AIMMS and the map is set by initializing it. We define the following mapping:

TemperatureMapping(dl::dt,dl::idn,dl::cn,dl::dn) := data {
( 'Average High', 'Countries'  , 1, 1 ) : "Country",
( 'Average High', 'January'    , 2, 0 ) : "Jan",
( 'Average High', 'May'        , 3, 0 ) : "May"
};


We named our string parameter TemperatureMapping and see in the above code that it is a parameter with four domains:

• dl::dt : This is the table name
• dl::idn : This is the identifier name
• dl::cn : This is the column number
• dl::dn : This is the domain number

The string value of data map TemperatureMapping is the column name and is initialized with the AIMMS function data.

The first element in our mapping we specify that we are looking in table “Average High”, which is the name of the work sheet in our xlsx file. Then we specify the name of the identifier in AIMMS. Note the subtle difference: the name of the set is “Countries” (plural), while the column name in the spreadsheet is “Country” (singular).

The column number is 1 and this is lower than that of the other entries of the data map. This is because this is a domain and has to be read first. We can see it is a domain because the domain number is 1 (non-zero). The other two entries have domain number 0, meaning that they are the parameters. Their domains are in this case the entry with domain number 1. Of cource in case of multi dimensional parameters the domain numbers of entries go 1, 2, 3 etc.

## The code¶

Now we have everything in place and can write the complete procedure of reading the data:

StringParameter TemperatureMapping {
IndexDomain: (dl::dt,dl::idn,dl::cn,dl::dn);
}
DeclarationSection Average_High_Declaration {
... (see above)
}
Body: {
empty Countries, January, May, TemperatureMapping;
dl::RemoveDataSourceMapping("TempAvHighMap");
TemperatureMapping,
dl::DependEmpty,
dl::TableAttributesEmpty,
dl::ColAttributeEmpty);
"TempAvHighMap",
}
DeclarationSection Local_Declaration {
IndexDomain: dl::rwattr;
}
}
}


Before we can run the code above we have to make sure that we added DataLink (with prefix dl) and the XLSProvider (with prefix xlsprov) to the project. In the code we see that we declare the data map TemperatureMapping as a string parameter, then we have the declaration section from above in which we declare the set Countries and the two parameters January and May.

The body of our ReadIt procedure starts with clearing all our identifiers to make sure we start of with a clean slate. We do not have to do it, if we want to add data from the data source we should not clear them.

Then we read from file the text file “datamapavt.txt” containing our data map specification. We could have initialized this in the declaration of string parameter TemperatureMapping, but using a text file allows us to store the mapping next to the data source. Also with larger data sources it is more convenient to toggle between different text files than modifying the initialization all the time.

In the next step we make sure that, if a mapping “TempAvHighMap” exists, it is cleared. The string “TempAvHighMap” is the name of the mapping used by DataLink to store the mapping. DataLink can store more than one data maps so we need the name to tell it which mapping to use. In the next line of code we create our ‘new’ mapping “TempAvHighMap” and pass our data map TemperatureMapping as second argument. The other three arguments are extra attributes, but in our code we use the empty defaults that are supplied by DataLink.

Then we create a string parameter ReadAttribute, which we declared locally in our procedure. We specify the 'DataProvider' and set this to xlsprovider::DataLink. This is an identifier supplied by the XLSProvider and contains the location of the code that has to run (the dll on windows).

We read data with the call dl::DataRead and pass the name of the data source, in this case the excel file “DataSource.xlsx”, as first argument. In the second argument we tell DataLink to use the mapping associated with the name “TempAvHighMap”. In the third argument we pass the ReadAttribute so that Datalink knows which provider to use. After this procedure is run, the identifiers specified in DeclarationSection Average_High_Declaration, will contain the data from the data source.