I am struggling to figure out this one as well.
I suppose it depends on how broadly acceptable you would your solution to be. If you are going to want to include datasets in your solution which might be scant on the details of the area (eg. perhaps a rural area or an area which just hasn't been mapped out properly), you most likely want to include all possible paths for a pedestrian, including main roads.
If however, you are dealing with rich and well defined data, the information you wish to include is defined within your mapconfig.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<type name="highway" id="1">
<class name="cycleway" id="118" />
<class name="footway" id="119" />
<class name="bridleway" id="120" />
<class name="byway" id="121" />
<class name="steps" id="122" />
</type>
</configuration>
To exclude certain road types from being imported, simply exclude the particular class from this XML file.
You can also include data on a place by place basis and import them into different databases with different map configs.