A request XML packet retrieving the list of all Web applications from Plesk Application Vault includes the get_all_packages_list operation node:
<packet version="1.4.2.0">
<siteapp>
<get_all_packages_list/>
</siteapp>
</packet>
The get_all_packages_list node has the following graphical representation:

Request packet sample
The request packet, that retrieves the list of all Web applications from Plesk Application Vault, looks as follows:
<packet version="1.4.2.0">
<siteapp>
<get_all_packages_list/>
</siteapp>
</packet>