A method of verifying permissioning rights to one or more data resources associated with a data processing platform , the method being performed using one or more processors and comprising: receiving, from a client device , an assertion statement identifying a user, a data resource and an operation performable with respect to the data resource; applying the received assertion statement to a network database storing an access control list defining, for each of a plurality of data resources (500, 602-604, 922-930) associated with the data processing platform , one or more users having permission to perform one or more operations on the respective data resource, wherein applying the received assertion statement comprises: determining a first data structure comprising an assertion tree for said data resource, the assertion tree comprising an expected hierarchical resource graph that represents permissions of the identified data resource and of one or more dependencies of the identified data resource, that would make the assertion statement true; determining a second data structure comprising a corresponding hierarchical resource graph that represents part of the access control list; and comparing the first data structure with the second data structure to determine if the assertion statement is true or false in relation to said data resource identified in the assertion statement; and in the event that the assertion is false, generating an error message for output. receiving, from a client device , an assertion statement identifying a user, a data resource and an operation performable with respect to the data resource; applying the received assertion statement to a network database storing an access control list defining, for each of a plurality of data resources (500, 602-604, 922-930) associated with the data processing platform , one or more users having permission to perform one or more operations on the respective data resource, wherein applying the received assertion statement comprises: determining a first data structure comprising an assertion tree for said data resource, the assertion tree comprising an expected hierarchical resource graph that represents permissions of the identified data resource and of one or more dependencies of the identified data resource, that would make the assertion statement true; determining a second data structure comprising a corresponding hierarchical resource graph that represents part of the access control list; and comparing the first data structure with the second data structure to determine if the assertion statement is true or false in relation to said data resource identified in the assertion statement; and determining a first data structure comprising an assertion tree for said data resource, the assertion tree comprising an expected hierarchical resource graph that represents permissions of the identified data resource and of one or more dependencies of the identified data resource, that would make the assertion statement true; determining a second data structure comprising a corresponding hierarchical resource graph that represents part of the access control list; and comparing the first data structure with the second data structure to determine if the assertion statement is true or false in relation to said data resource identified in the assertion statement; and in the event that the assertion is false, generating an error message for output. <EOS>