1International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

How to Pay in LicenseScript

C. N. Chong, S. Etalle, and P. Hartel

Universiteit Twente, The Netherlands

chong@cs.utwente.nl

2International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Overview

• Introduction

• Motivation

• LicenseScript Language

• LicenseScript Wallet

• Payment Policies

• Examples

• Conclusions and Future Work

3International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Introduction

• Most rights expression languages (RELs) specify rights, terms and conditions.

• But, they are not designed to capture payment management.

• We have proposed LicenseScript.• We have modeled payment with a simple

wallet in our previous work, but:– It is unrealistic.– It is inflexible.

4International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Motivation

• To investigate another application domain of LicenseScript.

• Thereby, to show the flexibility of the LicenseScript.

• To model the payment from the user’s perspective.

5International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Motivation (cont’d)

• We model the payment with LicenseScript.

• This is useful to verify the payment policies designed.

• How the payment is made, i.e., the underlying implementation details are abstracted by using primitives at the moment.

6International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

LicenseScript Language

• License consists of three parts: content, clauses, and bindings.

• Clause is a Prolog program to decide if the operation is allowed.

• Bindings store license data.

• Rule can be thought of as firmware of a system.

Bcontentlic ,,( License

.}

),,_,(_

),( -: )({

21

2

1

IdId

IddomaininBvalueget

IdidentifyBcanplay

Clause

pubkey}_{ domaininB Binding

)(

),,(),,(

:)(

Bcanplay

BVideolicBVideolic

Videoplay

Rule

7International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Wallet

• Wallet takes the following form:

• Γ is a set of Prolog clauses.

• B is a set of bindings.

type=bankaccount, money=1500,currency=euro, interest=0.5,bankcharge=1

wallet

canload(B1,B2,A):- get_value(B1,money,M), set_value(B1,money,M+A,B2), cantransfer(B1,B2,P,A):- get_value(B1,money,M), get_value(B1,bankcharge,C), C+A<=M, transfer(P,A), set_value(B1,money,M-(A+C),B2)

),( Bwallet

8International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Wallet (cont’d)

• We gather all the wallets of a user in a wallet manager.

• Ψ contains clauses that operate over wallets, for instance add_wallet and remove_wallet.

• L is the list of wallets.

),( Lwm

9International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Payment Policies

• The payment policies aid in deciding how to perform the payments.

• We need a weight predicate, s.t. weight is a real number in {0,1} inclusive, i.e., p(wallet,weight).

• Given the list of wallets L from wm(Ψ,L), we say that payment policy policy selects wallet wallet(Γ,B) for payment if predicate p(wallet(Γ,B),W) and W is a maximum weight.

10International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Brief Implementation Procedure

• Weight predicate p(Wallet,Weight) assigns weight Weight to wallet Wallet.

• Clause select(List,Charge,Wallet) will select wallet Wallet with maximum weight according to predicate p that has enough money to pay Charge, from List.

11International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Examples

• We can model various payment policies for different scenarios.

• We can define the predicate p how to assign the weight according to different scenarios.

• Example 1: Minimum bank charge.

• Example 2: Paying with loyalty points (e.g. air-miles, money coupon, and bank account).

12International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Conclusions and Future Work

• We have proposed a technique to model and specify payment policies to optimize payment strategies from user’s perspective in LicenseScript.

• We believe this technique blends smoothly with the LicenseScript framework, demonstrating its flexibility.

• Future Work:1. To modify select clause.

2. To specify selection policy.

13International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Rule

).'),',(

),,(,(_|

),,,',(|

)),,(,,(|

),,,',(|

)',(),(),',,(

),(),(),,,(:)(

LEwallet

EwalletLvalueset

CPEErcantransfe

EwalletCLselect

PCBBcanplay

LwmpolicyBXlic

LwmpolicyBXlicXplay

14International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Implementation I

select(L,C,W) :- map(L,L’), sort(L’,L”), choose(L”,C,W).

• map(L,L’) – returns L’ s.t.

L’={(w,weight)|w in L ^ p(w,weight)}

• sort(L’,L”) – sorts list L’ in L”, s.t.

L”={(w1,weight1),…,(wn,weightn)}, where weighti >= weighti+1, for i=1,…,n

15International Workshop for Technology, Economy, Social and Legal Aspects ofVirtual Goods 2004, May 27-29 2004 Ilmenau, Germany

Implementation II

• choose([H|T],C,H) :-H = wallet(_,B),get_value(B,money,M),M >= C.

choose([H|T],C,Y) :-choose(T,C,Y).

Choose the 1st wallet in the list that has enough money (in W’s money binding) to pay C.