02-first-model.md

2. Your first model

In this chapter you declare a part, give it values, instantiate it and inspect the result, first at the interactive prompt and then from a file. Everything shown is the same notation you would write in a .sysml file; the REPL just shows you the result sooner.

At the prompt

Launch the interactive REPL:

$ sysml
SysML v2 REPL — %help for commands, Ctrl-D to exit
sysml> 

Define a Simple Part

Library types such as Real are not in scope automatically. Import them exactly as a .sysml file would:

sysml> private import ScalarValues::*;
✓ import ScalarValues::*

sysml> part def Wheel {
  ...>     attribute diameter : Real = 16.0;
  ...>     attribute width : Real = 7.5;
  ...> }
✓ part def Wheel

Each accepted declaration is echoed back as ✓ <kind> <name>. An opening brace starts a continuation prompt (...>) that lasts until the matching closing brace. A blank line ends the submission, so don't put one inside a declaration you are typing.

Typing a namespace again adds to the one already in the session: submitting package P { part def B; } after package P { part def A; } leaves both declared. An empty body (package P { }) clears the namespace. Whenever a submission drops something, a note: line says what: the members no longer declared, the instances that became invalid (their IDs restart with the new model), and any %action or %state debugging session that was ended. A debugging session over a declaration the submission did not touch keeps running.

Define a Vehicle

sysml> part def Vehicle {
  ...>     attribute mass : Real = 1500.0;
  ...>     part wheels : Wheel[4];
  ...> }
✓ part def Vehicle

Instantiate and Inspect

sysml> %instantiate Vehicle
✓ Created instance of Vehicle
  ID: 1
  Use %features Vehicle to inspect

sysml> %features Vehicle
Instance: Vehicle (ID: 1)
Features:
  mass = 1500.0
  wheels = [Instance(ID: 2), Instance(ID: 3), Instance(ID: 4), Instance(ID: 5)]
    diameter = 16.0
    width = 7.5
    diameter = 16.0
    width = 7.5
    diameter = 16.0
    width = 7.5
    diameter = 16.0
    width = 7.5

sysml> %instances
Instances:
  Vehicle (ID: 1)

Evaluate Expressions

sysml> attribute wheelCount = 4;
✓ attribute wheelCount

sysml> attribute totalDiameter = wheelCount * 16.0;
✓ attribute totalDiameter

sysml> %eval totalDiameter
✓ totalDiameter
  = 64.0

---

From a file

Create a file my_model.sysml:

package MyModel {
    part def Sensor {
        attribute reading = 0.0;
        attribute threshold = 100.0;
    }

    part def System {
        part sensors : Sensor[3];
    }
}

Load the file in the REPL. %load submits the file's contents as if you had typed them, so it reports the same ✓ lines. %list prints everything the session currently holds:

$ sysml
sysml> %load my_model.sysml
✓ package MyModel

sysml> %list
package MyModel {
    part def Sensor {
        attribute reading = 0.0;
        attribute threshold = 100.0;
    }

    part def System {
        part sensors : Sensor[3];
    }
}

sysml> %instantiate MyModel::System
✓ Created instance of MyModel::System
  ID: 1
  Use %features MyModel::System to inspect

sysml> %features MyModel::System
Instance: MyModel::System (ID: 1)
Features:
  sensors = [Instance(ID: 2), Instance(ID: 3), Instance(ID: 4)]
    reading = 0.0
    threshold = 100.0
    reading = 0.0
    threshold = 100.0
    reading = 0.0
    threshold = 100.0

A composite feature lists the features of each of its objects beneath it, in order.

---

Next: 3. From the command line, which runs these same checks without a prompt. The prompt itself is covered in 4. The REPL.