1    Objective

As mentioned earlier these tutorials are focussing on providing the basic skills of knowledge engineering. In this first tutorial, the main dimensions of a ship will be systematically varied. The knowledge used is Archimedes’ Law in combination with design requirements, which are the following:

The ship should have

• a displacement of at least 2000 t, but less than 3000 t;
• a draft of 6 m.

Our objective is to generate a dataset of systematically varied ships that meet the design criteria.

2    Before we start

Before starting with your knowledge engineering, please make sure you are actually using the knowledge engineering user level and you have Quaestor configured in the most convenient layout.

To check/change your user level go to the general tab of  Tools>Options. You can change your User level. If you are not able to change it to Knowledge Engineer (level 3), you do not have KE rights. Please contact your ICT department or Qnowledge for the proper license.

Furhtermore, for editing all kinds of properties it is convenient to use the Frame Viewer. Therefore in the  Appeareance tab of Tools>Options select "Use classic frame viewer".

3    Creating parameters

When Quaestor is started, an empty knowledge base is automatically created. 

 In the Knowledge browser, minimize the Quaestor node, and expand the NewQkb node (figure 1).

Figure 1    Expanding the Newqkb node

When the knowledgebase node is expanded, the classes within the knowledgebase are visible. Classes are used to organise your parameters, and put them in a practicable structure. The Top Goals/Undefined class is part of the knowledge base by default. Here, the goal parameters of your calculation (Top Goals) can be stored, as well as other parameters that don't belong to other classes (Undefined).

We'll create a new class named Main Dimensions, in which the following ship parameters are to be stored.

•     Lpp: Length between perpendiculars
  
  
•     B: Moulded breadth
  
  
•     T: Draught from keel to Construction Water Line
  
   In the Knowledge browser  Top Goals/Undefined and select new Class (Ctrl+N). Provide the class with the name Main Dimensions. Note that the input box will already contain the word "Goals". To make a new class, delete Goals and write your class name (in this case Main Dimensions). Sub classes can be defined by adding the main class with sub classes separated by points: Goals.Sub goal

Figure 2    Creating a new class in the knowledge base 

The class is now shown in the knowledgebase tree, and we can add the parameters Lpp, B and T.

 Select the class Main Dimensions.  in the right-hand side of the knowledge browser, and select New Parameter/Function(Ctrl+I), see figure 3. Note that the last parameter in focus will be shown in the input field (most probably QKnowledgebaseVersion). Delete this parameter, type Lpp and click the Value button. Repeat these actions for the parameters B and T.

Figure 3    By right clicking in the right-hand side of the knowledge browser, parameters can be added 

The added parameters all appear like this:

The red cross is a sign that the parameter is not yet fully defined for the system.
In Quaestor, a valid parameter has:

• A unique name;
• A dimension (or assigned dimensionless);
• A way to be determined: input from the user or defined by a relation.

The first requirement is already satisfied, so let's assign dimensions to the parameters.

 Select the Lpp in the Knowledge Browser. In the Frame Viewer, change the ? sign to m, the dimension for Lpp (meters). A list of possible dimensions is automatically shown when you type.

In the larger area of the Frame Viewer, a reference can be assigned to the parameter. A proper reference is important, as users of the knowledgebase may not be certain of the exact meaning of the parameter. Please also read Documentation of knowledge for more details.

 Provide Lpp with the reference Length of the ship (figure 4).

Figure 4   In the Frame Viewer, a dimension and reference can be assigned to the parameter

NOTE: The dimension of a parameter can also be assigned in the Slots & Properties window. Just scroll down to the Dimension row, and change the value.

  Assign a dimension and a reference to the other parameters B and T, just as described above. Of course, the breadth and depth of the ship are defined in meters.

Now only the last requirement for valid parameters has yet to be fulfilled:

•  A way to be determined: input from the user or defined by a relation.

This qualification can be provided in the Slots & Properties window.

 Select the parameter LPP. In the Slots & Properties window, scroll down to the Determined by row. Change the value to VR: User only, as the parameter LPP is input (instead of defined by a relation), see figure 5.

Figure 5    Let Quaestor know how a parameter should be determined     

Notice that the status of LPP has changed to

to show that Quaestor knows enough about this parameter to use it in a computational model.

 Make sure that B and T are determined by VR (Value Requested):User only too.

Note that above you have explicitly added Lpp, B and T as parameters to the knowledge base. 
You are also able to implicitly add parameter by creating relations that contain new parameters. Quaestor will automatically add these new parameters to your knowledge base (so implicitly). You will see this next.

4    Creating relations

In order to define the loading capacity of the ship, it’s important to know the kind of water (Salt or Fresh) the ship will sail in. Therefore, we will add some relations and constraints, and make sure the user can select the watertype.

We'll add two relations, one for salt water and one for fresh water.

  Select Top Goals/Undefined in the knowledge browser,  in the right hand side and select New Relation (Ctrl+N). In the upper part of the new window, delete any proposal (Quaestor may have filled in the last selected parameter), and enter

(belonging to salt water), and press Save (figure 6).

 Figure 6   Entering a relation 

Note that when you enter a relation, Quaestor provides as much help as possible by means of the Help Checker. This checker shows what to expect (in this case a Value or an Expression, ValExp).  After saving a relation, the Help Checker will check the syntax for possible errors, and shows a warning message when something is wrong.

Because of entering the relation, the parameter Rho has automatically been created. Furthermore, note and realise that the parameter is created in the Class in focus when saving the relation. For Rho to be a valid parameter, a dimension should be assigned.

  Provide a reference for rho and assign it the dimension kg/m^3. Rho is now a valid parameter. Furthermore, make sure rho is determined by SYS: System/Equation, as a relation is used to determine rho.

The following might seem a bit unconventional: a second relation is given for Rho. This is a nice example of how quaestor works: In a calculation, Quaestor can find numerous calculation paths and automatically chooses the most appropiate one based on constraints and available data. An infinite number of relations can be assigned to one particular parameter.   

  Add the following relation (belonging to fresh water) in a similar way as described above

5    Creating constraints

The two relations for the density of the water are only valid for their corresponding watertype. Therefore, a constraint is added to each relation. A constraint is simply a restriction for the validity of the relation.

  Double click Top Goals/Undefined in the knowledge browser: all relations in that class are shown (this will work for any class). One can always edit a relation by selecting it and pressing F2 (or  and select edit). This is also a useful method to find out which relation you actually selected.

Now  the relation Rho = 1025 and select Constraint->Add New. In the upper part of the new window enter the following constraint:

and press Save (figure 7).

Figure 7   Adding a constraint to a relation

The constraint is now added, and a parameter named Watertype$ has been created. The $ at the end of the parameter name makes sure Quaestor recognizes it as a String value, and the dimension Str is automatically assigned (see also Quaestor syntax. We have to assign a determined by value to make it a valid parameter.

  Make sure Watertype$ is determined by VR: User Only, as the user should provide the information concerning the water type.

We repeat the process for the other relation: 

  Add the constraint: Watertype$ = "FW" to the relation Rho=998. Note that the expression editor assist you with the presentation of existing parameters and intrinsic function. When you press enter while an existing parameter or function is blue, this parameter or function is placed in the expression editor.

Both relations are now connected to the corresponding watertype by means of the value of the string Watertype$. Note if Rho is needed in the calculation progress, Quastor will note that the watertype is needed and will ask the user for this value (because it is assigned User Only).

TIP: By selecting a parameter in the knowledge base and then double clicking the box below the knowledge base tree, the relations defining that particular parameter are visible (figure 8).
Moreover, when you select a relation in the knowledge base, and double click that box, the parameters that can be calculated by the selected relation are shown.
When single clicking the box, all connections to the parameter or relation are shown. See also information on the Knowledge Browser.

 Figure 8   When selecting a parameter and double clicking the box indicated by the blue arrow, all relations defining that parameter are shown.

6    Creating a dropdown menu

Because there are only two possible values for Watertype$ (SW or FW), it's easy to integrate a dropdown box. 

   Select Watertype$ in the knowledge browser, and add the following text as reference text in the frame viewer (figure 9):

Figure 9   A dropdown box is created by entering this information in the reference slot of the frame viewer

The use of a dropdown box will be clear in a later stage of this tutorial, when calculations are made. Note that you can add the @EQEXPLAIN attribute to the data slot of the Watertype$ parameter (see Frame Viewer for data slot)  in order to manipulated that only "Saltwater" and "Freshwater" are shown (so without SW and FW).

7    Creating a relation for the displacement

On the basis of the earlier defined parameters and the block coefficient Cb , the displacement of the ship can be calculated.

   Add the following relation to the class Main Dimensions:

which defines the displacement of the ship in tons

Note that two new parameters are created: the block coefficient Cb and the displacement DISP. In order to keep the knowledgebase meaningful, it is necessary to provide references, dimensions and determined by values for these parameters.

  Provide references, dimensions and determined by values for Cb and DISP. Cb has no dimension (-), DISP should be in tons (t). Just press ok if Quaestor notes that tons is no base dimension (kg), it is just to inform you. We covered this by dividing DISP by 1000. The determined by values should be VR: User Only for Cb, and SYS: System/Equation for DISP, as the block coefficient is input and the displacement is determined by a relation.

8    Creating a solution

Let's perform our first Quaestor calculation. A solution is always determined by one or more Top Goals. A top goal is a parameter (or object) that is your final calculation target, in this tutorial it's the displacement of the ship. 

   Select the class Main Dimensions in the knowledge browser. Double click the parameter DISP.

Note that the  sign of DISP changed to , indicating that it's a top goal for the calculation.

Calculations and solutions are managed in the workbase. Here, solutions can be created, redone (with different data), examined and deleted. 

  In the workbase, click the  button when you use classic buttons or the "Create Solution" button when you use the Workbase buttons to start the calculation with top goal DISP.

The calculation progress is started, and Quaestor first collects all input data (figure 10).

 Figure 10   Input data for the calculation

Entering data is easy: just type a value for each selected parameter and press enter to switch to the next one.

  Enter the following data for our first calculation:

Note that the input of Watertype$ consists of a dropdownbox, which we created in (4), see figure 11. 

 Figure 11   Watertype$ can be selected in a dropdownbox

After providing the data you have to press the  button or "Accept input & Continue" button to continue. The actual calculation is started now, and the right-hand side of the workbase shows the situation of figure 13. During the calculation, the box indicated with the blue arrow shows the status of the calculation.

Because this is a very simple example, the final state is alost immediately shown.

Figure 13   Status of the calculation and solution

The top goal (DISP) is shown, together with all parameters that were used for the calculation. With these input values, the displacement of the ship is about 2030 tons.

9    Multiple case solutions

So far, we created one solution, which is shown in the workbase (figure 14).

 Figure 14   All solutions are shown in the workbase 

As mentioned in the objective, we'd like to create a dataset of systematically varied ships. We could of course perform several calculations with different input data by hand, but it's much easier to use the ability of Quaestor to create multiple case solutions. To keep the complexity of this example within reason, we will only vary the breadth and length of the vessel. Please note that due to some important conceptual reasons the latest Quaestor release can only perform calculations on ranges of parameters when you alreade have created a solution.

   In the workbase, select the solution you have already created (called the same as the top-goal parameter DISP). Restart the solution by pressing the  or "Redo Solution" button in the workbase. Quaestor will present the previous input, change the following input:

B= 9(0.5)11 m    Lpp= 55(2)69 m

In this way, B and Lpp are defined by a range, given the start value, step size and end value. For example, Lpp is defined from 55 to 69 meter, with steps of 2 meter.

Quaestor will ask if it should create a case matrix for Lpp (figure 15), click yes (an explanation will follow).

Figure 15    Quaestor asks if a case matrix should be created 

You will see that the single value input is still in the list and the multi case values are in the table part of the Workbase. Press the button or "Accept input & Continue" button to continue.

The new solution is now created. The fixed values are again shown in the right hand side of the workbase. The varying parameters (B and Lpp) and the corresponding solution for DISP are shown in the lower part. Each row is a different case, identified by a case number(#1, #2, etc.), see figure 16.

Figure 16    Multiple case solutions are shown in the workbase, each row is a different case 

What does the Case matrix question mean?  Note that the variations of B do not correspond to the variations of Lpp: there are 5 values for B and 8 values for Lpp. If we would have answered No to the Case matrix question, five variations of B would have been made, each one with the corresponding value of Lpp (the last 3 Lpp values would be omitted). In that way, there would be only five cases. As we answered Yes to the question, all possible combinations are considered, which results in 5*8=40 cases. You can easily notice the difference by creating a new solution with the same input values, but now answer no to the case matrix question.

NOTE: Ranges can be defined in multiple ways: 

• Individual values can be separated by comma’s: 9, 10, 11 or, when in the Modeller tab of Tools>Options you have selected "Use ";" instead of "," in range input", the separation is by means of a semi colon (;);
• You can define a range with a begin, an end and number of steps (intervals): 9(&2)11;
• You can define a range with a begin, an end and a step size: 9(1)11;
• You can define a range with a begin, an end and a step size, including the last element when this is smaller than the whole amount of steps: 9(#1)11.5;

10    Manage solutions

Our multiple case solution table is sorted by the breadth of the ship, as shown in figure 16. Suppose we'd like parameter Lpp the leading parameter in this table.

    In the knowledge browser, select the parameter Lpp. In the Slots & Properties window, scroll down to the row Output to, and select HEADER (figure 17). Now, refresh the table of the multiple case solution by clicking another solution, and then again the multiple case solution. The table is now leaded by Lpp.

 Figure 17   By selecting Output to HEADER, the parameter will 'lead' the multiple case solution table

A lot of cases in our solution don't meet the design criteria: a displacement between 2000 and 3000 ton. We could have fixed this by adding a constraint to DISP, but another way is to use a filter in the solution table.

   In the workbase, select the last (multiple case) DISP solution, and click the   or "Filter" button. The filter window shows. For DISP, select Range as filter, fill in 2000 for Lower bound and 3000 for upper bound (figure 18). Click the Apply button.

 Figure 18   With a filter, cases that do not fulfill the filter conditions can be made invisible

Now, only the cases for which 2000<DISP<3000 are shown in the table. Our objective has been completed:  we build a dataset of systematically varied ships that meet the design criteria.

11    Check

You can verify your results by comparing it to [Tutorial 1 Finished] 

Continue to tutorial 2 >>