Enabling Write Back you can override the mapped value in the Properties Palette, Data Manager, or PlantDataManager.

Let's enable Write Back for the Description property.

Here we see die mapped data for both pumps.

Now we select just one pump and we change the Description.

When we save the drawing now, The previous mapped Description for the second pump is no out-of-date and therefore PlantLink wants us to select/update the data again.

Now the Description for the second pump has been updated.

By default, Clear Value is enabled, it means, that if PlantLink cannot find a suitable row in the table or view, or the user didn't select anything, then any value in the property will be deleted. This ensures, that there are no old values from previous mappings.

This option can be used with or without a condition. A condition defines when a value should be cleared.

For this example, we disable the checkbox Clear Value for the Model Number property.

If you change the type to a value for which there are no rows available, all properties with the exception of the Model Number are cleared.

When selecting P again, the PlantLink - External Data Viewer dialog pops up again and you can select a row.

The old 0001 value will be overridden with the new value.

Now we will define an expression. What we want to accomplish is, that the Model Number will be cleared only, if Manual Data is set to Yes. This allows you to later enter a value for Model Number which will not be cleared.

For that you click on the square button right of the checkbox for Clear Value.

The Expression Editor opens.

We use the following expression. This expression means, that if the property Manual Data shows no, the condition is True, otherwise it's False. Meaning, that if Manual Data is No the value in Model Number will be cleared. Otherwise the value will not be cleared.

You can see the expression also in the tooltip.

Let's start with this case were data are mapped and Manual Data is No.

When we select a Type for which there are no data, the Model Number is cleared.

Now we select P again and select a row from the PlantLink - External Data Viewer. And now we change Manual Data to Yes.

If we select a type again for which there are no data, then the Model Number value stays.

If a property is acquired, then PlantLink cannot map a value to this property. By default Acquisition Mode Override is disabled. When enabling this option PlantLink will change the Acquisition Mode to Override before mapping the value to the property. If the Acquisition Mode is set to Override and the mapped value is the same as the acquired value would be, then PlantLink will change the Acquisition mode back to Acquire.

For this example, we have a second link configuration in this project for the Hand Valves class.

In the mapping page of the Wizard we check Override Acquisition Mode.

In the drawing we see, that the Ball Valve acquires the Size from the PipeLineSegment.

If we use Assign Data from the context menu of the valve symbol we now select a valve with a different size as the PipeLineSegment.

We see the new Size on the valve symbol and we see, that the Acquisition Mode for the Size property for the ball valve is set to Override.

Now we select a row from the table where the Size matches the Size of the PipeLineSegment.

Now we see, that the Acquisition Mode is set back to Acquire.

Sync Mode controls when the mapped properties will be updated. Although PlantLink will instantly map the properties whenever you change the values used in the linked expression, there are cases where you might want to ensure, that the mapped properties are updated. The options are:

1.Never                        Mapped properties will not be updated. Unless you use Update Link Configurations

2.On Drawing Open        Mapped properties will be updated when the drawing is opened

3.On Drawing Save        Mapped properties will be updated when the drawing is saved

The list option is the commonly used one, because it ensured, that the mapped properties are always up-to-date when saving, or saving&closing a drawing