Data Initialization

Separation of model and data

In the previous section the entire depot location model was specified without any reference

• to specific elements in the sets Depots and Customers, or

• to specific values of parameters defined over such elements.

As a result of this clear separation of model and data values, the model can easily be run for different data sets.

Data sources

A data set can come from various sources. In AIMMS there are six sources you might consider for your application. They are:

• commercial databases,

• text data files,

• AIMMS case files,

• internal procedures,

• external procedures, or

• the AIMMS graphical user interface (GUI).

These data sources are self-explanatory with perhaps the AIMMS case files as an exception. AIMMS case files are obtained by using the case management facilities of AIMMS to store data values from previous runs of your model.

A simple data set in text format

The following fictitious data set is provided in the form of an text data file. It illustrates the basic constructs available for providing data in text format. In this file, assignments are made using the ‘:=‘ operator and the keywords of DATA TABLE and COMPOSITE TABLE announce the table format. The exclamation mark denotes a comment line.

  Depots    := DATA { Amsterdam, Rotterdam };
  Customers := DATA { Shell, Philips, Heineken, Unilever };

  COMPOSITE TABLE
      d        DepotRentalCost    DepotCapacity
! ---------    ---------------    -------------
  Amsterdam        25550              12500
  Rotterdam        31200              14000
;

  COMPOSITE TABLE
      c        CustomerDemand
! ---------    --------------
  Shell            10000
  Philips           5000
  Heineken          3000
  Unilever          5000
;

  Distance(d,c) := DATA TABLE
                Shell   Philips   Heineken   Unilever
  !             -----   -------   --------   --------
  Amsterdam      100      200        50         150
  Rotterdam       75      100        50          75
  ;

  UnitTransportRate   := 1.25 ;
  MaxDeliveryDistance := 125  ;

Reading in the data

Assuming that the text data file specified above was named "initial.dat", then its data can easily be read using the following READ statement.

read from file "initial.dat" ;

Such READ statements are typically placed in the predefined procedure MainInitialization. This procedure is automatically executed at the beginning of every session immediately following the compilation of your model source.

Automatic initialization

When AIMMS encounters any reference to a set or parameter with its own definition inside a procedure, AIMMS will automatically compute its value on the basis of its definition. When used inside the procedure MainInitialization, this form of data initialization can be viewed as yet another data source in addition to the six data sources mentioned at the beginning of this section.