Mortgage Monthly Payment Table

BPMN & Modeling Discussion & Questions
1

Good evening.

I’m working in a Bank and we are evaluating bpmn and dmn tools in the market for our new Online Mortgage System.
For the PoC we are doing a very very simple Mortgage Simulator.
The question regarding with the dmn / bpmn is how to obtain in Camunda a Mortgage Monthly Payment Table output.

Thank you in advanced

Best regards,
JE

2

Hi @Jose_Enrique_Perez_F,

happy to hear that you want to base your implementation on Camunda.

Do you have any specific question about DMN?

Please have a look at the DMN Get Started guide: https://docs.camunda.org/get-started/dmn11/

Best regards,
Philipp

3

Hi Philipp,

Yes, we read the BPMN and DMN started guides, even, we bought the book Real-Life BPMN Book and we were playing with the platform for a few days.

The specific question is the following:

1.- Business department give us the process definition about Mortgage Simulator.

2.- We expected obtain the following from of the Simulation:

17
171820×918 383 KB

We map the requirements in point 1 to a Camunda BMPN model to be executed in Camunda but to obtain the Amortization Schedule on the right (Monthly Payment):

public List<Payment> calculatePaymentList(Date startDate, double initialBalance, int durationInMonths, int paymentType, double interestRate, double futureValue)
{
    List<Payment> paymentList = new ArrayList<Payment>();
    Date loopDate = startDate;
    double balance = initialBalance;
    double accumulatedInterest = 0;
    for (int paymentNumber = 1; paymentNumber <= durationInMonths; paymentNumber++)
    {
        if (paymentType == 0)
        {
            loopDate = addOneMonth(loopDate);
        }
        double principalPaid = paymentService.ppmt(paymentService.getMonthlyInterestRate(interestRate), paymentNumber, durationInMonths, initialBalance, futureValue, paymentType);
        double interestPaid = paymentService.ipmt(paymentService.getMonthlyInterestRate(interestRate), paymentNumber, durationInMonths, initialBalance, futureValue, paymentType);
        balance = balance + principalPaid;
        accumulatedInterest += interestPaid;

        Payment payment = new Payment(paymentNumber, loopDate, balance, principalPaid, interestPaid, accumulatedInterest);

        paymentList.add(payment);

        if (paymentType == 1)
        {
            loopDate = addOneMonth(loopDate);
        }
    }
    return paymentList;
}

/**
* Emulates PMT(interest_rate, number_payments, PV, FV, Type) function, which calculates
* the mortgage or annuity payment/yield per period.
*
* @param r periodic interest rate represented as a decimal.
* @param nper number of total payments or periods.
* @param pv present value – borrowed or invested principal.
* @param fv future value of loan or annuity.
* @param type when payment is made: beginning of period is 1; end, 0.
* @return double representing periodic payment amount.
*/
public double pmt(double r, int nper, double pv, double fv, int type)
{
if (r == 0) {
return -(pv + fv) / nper;
}

    // i.e., pmt = r / ((1 + r)^N - 1) * -(pv * (1 + r)^N + fv)
    double pmt = r / (Math.pow(1 + r, nper) - 1) * -(pv * Math.pow(1 + r, nper) + fv);

    // account for payments at beginning of period versus end.
    if (type == 1) {
        pmt /= (1 + r);
    }

    // return results to caller.
    return pmt;
}

/**
* Emulates IPMT(interest_rate, period, number_payments, PV, FV, Type) function, which calculates
* the portion of the payment at a given period that is the interest on previous balance.
*
* @param r periodic interest rate represented as a decimal.
* @param per period (payment number) to check value at.
* @param nper number of total payments or periods.
* @param pv present value – borrowed or invested principal.
* @param fv future value of loan or annuity.
* @param type when payment is made: beginning of period is 1; end, 0.
* @return double representing interest portion of payment.
* @see #pmt(double, int, double, double, int)
* @see #fv(double, int, double, double, int)
*/
public double ipmt(double r, int per, int nper, double pv, double fv, int type)
{
// Prior period (i.e., per-1) balance times periodic interest rate.
// i.e., ipmt = fv(r, per-1, c, pv, type) * r
// where c = pmt(r, nper, pv, fv, type)
double ipmt = fv(r, per - 1, pmt(r, nper, pv, fv, type), pv, type) * r;

    // account for payments at beginning of period versus end.
    if (type == 1) {
        ipmt /= (1 + r);
    }

    // return results to caller.
    return ipmt;
}

The problem is we don`t able to understand how to invoke this in the bpmn/dmn process and return the List.

Thank you in advanced

Best regards,
JE

4

I’m sorry but I don’t see your problem. It seems that you have exactly one method that you want to invoke in the process, right?

You can use a service task to invoke the class/method. Please have a look at the documentation: https://docs.camunda.org/manual/7.10/reference/bpmn20/tasks/service-task/#calling-java-code

1 Like