1. Data exchange system comprising multiple data processing units (4, 5) comprising multiple portable data processing units and multiple non-mobile data processing units, said portable data processing units being arranged to establish a temporary communication link (6) with at least one other data processing unit and said non-mobile are arranged to establish a permanent communication link (6), communications along said communication links being synchronous, each of said data processing units (4, 5) comprising data communication means (7, 14), processing means (8, 15) and memory means (9, 16), the latter comprising an executive program (12, 17), wherein the memory means (9, 16) of the totality of the processing units further comprises descriptions of the possible modes of communication between the data processing units as interaction contexts (11(1) . . . 11(m), 19(1) . . . 19(m)) in accordance with the following data structure:a. a set of basic distinct communication primitives (A(1) . . . ) which are distinct values and are accepted as commands upon receipt thereof by any of said data processing units (4, 5) during communications with at least one other of said data processing units (5, 4); b. a set of procedural descriptions (C(1) . . . ) defining procedures to be performed by any of said data processing units (4, 5) in response to accepted communication primitives (A(1) . . . ); c. a set of data elements (H(1) . . . ) distributed over said multiple processing units (4, 5), which are either permanently stored or computed and which are available for use when the procedures as defined in the procedural descriptions (C(1) . . . ) are performed, the use of and the access to said data elements being controlled; d. a first set of references (r(1), r(2), r(3)) to said data elements (H(1) . . . ), said references of said first set (r(1), r(2), r(3)) being associated to the procedural descriptions (C(1) . . . ) such that said data elements are available for use when procedures as defined in the procedural descriptions (C(1) . . . ) are performed; e. a possible second set of references (r(4), r(5), r(6)) to said data elements (H(1) . . . ), said references of said second set (r(4), r(5), r(6)) being associated to procedural descriptions (C(4) . . . ) of possibly further interaction contexts, such that said data elements are available for use when procedures as defined in procedural descriptions (C(1) . . . ) of said possibly further interaction contexts are performed; f. a, possibly empty, first data list (B(1) . . . ) comprising a possibly ordered third set of references (u(1) . . . ) to said data elements (H(1) . . . ), said third set of references (u(1) . . . ) being available as targets for references of a fourth set of references (w(1) . . . ), said references of said fourth set (w(1) . . . ) being part of said communication primitives (A(1) . . . ), which data elements are to be used by the procedural descriptions (C(1) . . . ) associated with said communication primitives (A(1) . . . ); g. a first set of access conditions associated to said data elements (H(1) . . . ), which conditions are consulted in association to said first set (r(1), r(2), r(3)) and second set (r(4), r(5), r(6)) of references to said data elements; h. a second set of access conditions associated to the third set of references (u(1) . . . ) in the first data list (B(1) . . . ).', 'a. a set of basic distinct communication primitives (A(1) . . . ) which are distinct values and are accepted as commands upon receipt thereof by any of said data processing units (4, 5) during communications with at least one other of said data processing units (5, 4);', 'b. a set of procedural descriptions (C(1) . . . ) defining procedures to be performed by any of said data processing units (4, 5) in response to accepted communication primitives (A(1) . . . );', 'c. a set of data elements (H(1) . . . ) distributed over said multiple processing units (4, 5), which are either permanently stored or computed and which are available for use when the procedures as defined in the procedural descriptions (C(1) . . . ) are performed, the use of and the access to said data elements being controlled;', 'd. a first set of references (r(1), r(2), r(3)) to said data elements (H(1) . . . ), said references of said first set (r(1), r(2), r(3)) being associated to the procedural descriptions (C(1) . . . ) such that said data elements are available for use when procedures as defined in the procedural descriptions (C(1) . . . ) are performed;', 'e. a possible second set of references (r(4), r(5), r(6)) to said data elements (H(1) . . . ), said references of said second set (r(4), r(5), r(6)) being associated to procedural descriptions (C(4) . . . ) of possibly further interaction contexts, such that said data elements are available for use when procedures as defined in procedural descriptions (C(1) . . . ) of said possibly further interaction contexts are performed;', 'f. a, possibly empty, first data list (B(1) . . . ) comprising a possibly ordered third set of references (u(1) . . . ) to said data elements (H(1) . . . ), said third set of references (u(1) . . . ) being available as targets for references of a fourth set of references (w(1) . . . ), said references of said fourth set (w(1) . . . ) being part of said communication primitives (A(1) . . . ), which data elements are to be used by the procedural descriptions (C(1) . . . ) associated with said communication primitives (A(1) . . . );', 'g. a first set of access conditions associated to said data elements (H(1) . . . ), which conditions are consulted in association to said first set (r(1), r(2), r(3)) and second set (r(4), r(5), r(6)) of references to said data elements;', 'h. a second set of access conditions associated to the third set of references (u(1) . . . ) in the first data list (B(1) . . . ).

2. Data processing unit of a data exchange system according to claim 33 and comprising multiple data processing units (4, 5), of which at least one is portable, said data processing unit (5) comprising data communication means (14), processing means (15) and memory means (16), the latter comprising an executive program (17), wherein the memory means (16) further comprises descriptions of the possible modes of communication between the data processing units as interaction contexts (19(1) . . . 19(m)) in accordance with the following data structure:a. a set of basic distinct communication primitives (A(1) . . . ) which are distinct values and are accepted as commands upon receipt thereof by said data processing unit (5) during communications with at least one other of said data processing units (4); b. a set of procedural descriptions (C(1) . . . ) defining procedures to be performed by said data processing unit (5) in response to accepted communication primitives (A(1) . . . ); c. a, possibly empty, set of data elements (H(1) . . . ) which are either permanently stored or computed and which are available for use when the procedures as defined in the procedural descriptions (C(1) . . . ) are performed, the use of and the access to said data elements being controlled; d. a, possibly empty, first set of references (r(1), r(2), r(3)) to said data elements (H(1) . . . ), said references of said first set (r(1), r(2), r(3)) being associated to the procedural descriptions (C(1) . . . ) such that said data elements are available for use when procedures as defined in the procedural descriptions (C(1) . . . ) are performed; e. a, possibly empty, second set of references (r(4), r(5), r(6)) to said data elements (H(1) . . . ), said references of said second set (r(4), r(5), r(6)) being associated to procedural descriptions (C(4) . . . ) of possibly further interaction contexts, such that said data elements are available for use when procedures as defined in procedural descriptions (C(1) . . . ) of said possibly further interaction contexts are performed; f. a, possibly empty, first data list (B(1) . . . ) comprising a possibly ordered third set of references (u(1) . . . ) to said data elements (H(1) . . . ), said third set of references (u(1) . . . ) being available as targets for references of a fourth set of references (w(1) . . . ), said references of said fourth set (w(1) . . . ) being part of said communication primitives (A(1) . . . ), which data elements are to be used by the procedural descriptions (C(1) . . . ) associated with said communication primitives (A(1) . . . ); g. a first set of access conditions associated to said data elements (H(1) . . . ), which conditions are consulted in association to said first set (r(1) r(2), r(3)) and second set (r(4), r(5), r(6)) of references to said data elements; h. a second set of access conditions associated to the third set of references (u(1) . . . ) in the first data list (B(1) . . . ) said data processing unit containing more than one interaction context, wherein at least one of the communication primitives accepted by said data processing unit will be to selectively indicate one of the said interaction contexts (19(1) . . . ) for further referral in said data processing unit.', 'a. a set of basic distinct communication primitives (A(1) . . . ) which are distinct values and are accepted as commands upon receipt thereof by said data processing unit (5) during communications with at least one other of said data processing units (4);', 'b. a set of procedural descriptions (C(1) . . . ) defining procedures to be performed by said data processing unit (5) in response to accepted communication primitives (A(1) . . . );', 'c. a, possibly empty, set of data elements (H(1) . . . ) which are either permanently stored or computed and which are available for use when the procedures as defined in the procedural descriptions (C(1) . . . ) are performed, the use of and the access to said data elements being controlled;', 'd. a, possibly empty, first set of references (r(1), r(2), r(3)) to said data elements (H(1) . . . ), said references of said first set (r(1), r(2), r(3)) being associated to the procedural descriptions (C(1) . . . ) such that said data elements are available for use when procedures as defined in the procedural descriptions (C(1) . . . ) are performed;', 'e. a, possibly empty, second set of references (r(4), r(5), r(6)) to said data elements (H(1) . . . ), said references of said second set (r(4), r(5), r(6)) being associated to procedural descriptions (C(4) . . . ) of possibly further interaction contexts, such that said data elements are available for use when procedures as defined in procedural descriptions (C(1) . . . ) of said possibly further interaction contexts are performed;', 'f. a, possibly empty, first data list (B(1) . . . ) comprising a possibly ordered third set of references (u(1) . . . ) to said data elements (H(1) . . . ), said third set of references (u(1) . . . ) being available as targets for references of a fourth set of references (w(1) . . . ), said references of said fourth set (w(1) . . . ) being part of said communication primitives (A(1) . . . ), which data elements are to be used by the procedural descriptions (C(1) . . . ) associated with said communication primitives (A(1) . . . );', 'g. a first set of access conditions associated to said data elements (H(1) . . . ), which conditions are consulted in association to said first set (r(1) r(2), r(3)) and second set (r(4), r(5), r(6)) of references to said data elements;', 'h. a second set of access conditions associated to the third set of references (u(1) . . . ) in the first data list (B(1) . . . ) said data processing unit containing more than one interaction context, wherein at least one of the communication primitives accepted by said data processing unit will be to selectively indicate one of the said interaction contexts (19(1) . . . ) for further referral in said data processing unit.', '3. Data exchange system according to claim 1 further characterized in that the set of the procedural descriptions (C(1) . . . ) at least comprises a first procedural description to be performed in response to the communication primitive, or primitives, which indicate one of the said interaction contexts (19(1) . . . ) for further referral in the processing unit accepting the communication primitives, such performance resulting in a proper activation of the indicated interaction context.', '4. Data exchange system according to claim 1 further characterized in that the memory means further comprises at least two interaction contexts (19(1) . . . ) and in that the set of the procedural descriptions (C(1) . . . ) at least comprises a last procedural description to be performed in response to the communication primitive, or primitives, which indicate one of the said interaction contexts (19(1) . . . ) for further referral in the processing unit accepting the communication primitive, such performance resulting in a proper deactivation of the interaction context which was indicated while the communication primitive was received.', '5. Data exchange system according to claim 1 characterized in that the memory means (16) further comprises at least two interaction contexts (19(1) . . . 19(m)), at least one application description (18(1) . . . ) and a memory element (20) storing a reference to the interaction context currently being in force, each application description comprising:a. a data list comprising references (E(1) . . . ) to data elements, which references may be accessible to two or more interaction contexts (19(1) . . . ) and may be extended by additional data elements; b. a further set of access conditions associated to said references (E(1) . . . ) or to said additional data elements and defining restrictions of use.', 'a. a data list comprising references (E(1) . . . ) to data elements, which references may be accessible to two or more interaction contexts (19(1) . . . ) and may be extended by additional data elements;', 'b. a further set of access conditions associated to said references (E(1) . . . ) or to said additional data elements and defining restrictions of use.', '6. Data exchange system according to claim 5 characterized in that each application description (18(1) . . . ) also comprises a procedure library comprising codes (F(1) . . . ) which can be used by procedural descriptions (C(1) . . . ) of each interaction context associated to each of said application descriptions (18(1) . . . ).', '7. Data exchange system according to claim 5 characterized in that the memory means comprises at least two application descriptions (18(1) . . . ) and units of executable code (G(1) . . . ) which can be used by procedural descriptions (C(1) . . . ) of each interaction context (19(1) . . . ) within each application description (18(1) . . . ) or by each unit of executable code (F(1) . . . ) of each procedure library within each application description (18(1) . . . ).', '8. Data exchange system according to claim 6 characterized in that the units of executable code in the procedure library are enhanced by including a specification of the use of their operational parameters into classes relating to attributes pertaining to data elements which can be passed as actual value in a computation, which computation only proceeds if the data attributes and parameter classes match.', '9. Data exchange system according to claim 5 characterized in that the executive program (17) comprises a reference to a default interaction context which is used to initialize the memory element (20) storing a reference to the interaction context currently being in force, in order to carry out a final action after a detection of an internal inconsistency in a recovery to a normal state of operation or whenever the executive program (17) is active and no explicit interaction context has been specified by a communication primitive received from a similar data processing unit (4).', '10. Data exchange system according to claim 1 characterized in that the executive program (17) comprises routines constituting an interpreter for coded instructions for an abstract processor, such that the majority of procedural descriptions (C(1) . . . ) and some of the units of executable code (F(1) . . . , G(1) . . . ) are coded in numeric values for interpretation by said interpreter routines.', '11. Data exchange system according to claim 6 characterized in that the procedural descriptions (C(1) . . . ) are encoded as indexes in a list over a sub set of procedures contained in the library of procedures comprising units of executable code.', '12. Data exchange system according to claim 11 characterized in that the encoding of the procedural descriptions (C(1) . . . ) is in such small values that more than one description can be held in a basic unit of access for the memory means (16) or that the description can be combined with other relevant information in the same basic unit of memory access.', '13. Data exchange system according to claim 12 characterized in that at least one of the encoding values of the procedural descriptions (C(1) . . . ) refers to a special function of the executive program (17) that is designed to select by indirection the actual function to perform for the encoded procedural description possibly by incorporating additional coding information stored in association with the procedural description encoded with said special values.', '14. Data exchange system according to claim 1 characterized in that the memory means (16) comprises an interaction context dedicated to comprise Personal Identification Numbers and that the executive program (17) is arranged to verify Personal Identification Numbers supplied by a user of the data exchange system.', '15. Data exchange system according to claim 1 characterized in that the memory means (16) comprises at least one interaction context dedicated to manage the number and content of other interaction contexts (19(1) . . . ) also contained in said memory means.', '16. Data exchange system according to claim 5 characterized in that each application description (18(1) . . . ) comprises a list of numeric values which is constructed to provide identifiers for all interaction contexts (19(1) . . . ) and comprises at least one of the following numeric values, a first indicating an application type, a second numeric value indicating a unique identification of the entity providing the application, a third numeric value indicating the nature of the application description (18(1) . . . ) and further numbers each uniquely referring to one interaction context (19(1) . . . ) associated with the application description.', '17. Data exchange system comprising multiple data processing units (4, 5) of which some, which are portable establish a temporary communication link (6) and of which others, which are not mobile may have a permanent communication link (6) said units comprising data communication means (7, 14), processing means (8, 15) and memory means (9, 16) the latter comprising an executive program (12, 17) characterized in that the communication means (14) is arranged to structure data exchange in blocks of data comprising at least two parts, a first part being data qualified as operational in that it is used to influence the nature of the operations performed by a command as indicated by a communication primitive or data resulting from operations carried out, a second part being qualified as security in that it is used to determine the appropriateness of performing an operation or of the acceptability of data within the operational part, to be used in the operation or to prove completion of the operation or correctness of the resulting data.', '18. Data exchange system according to claim 17 characterized in that the executive program (17) is arranged to perform, upon accepting a communication primitive to perform operations specified in the current interaction context (19(1) . . . ), each operation as part of a predetermined and fixed sequence of actions each of which is specified separately as part of a procedural description associated to the accepted communication primitive, which procedural description at least comprises distinct descriptions, any of which may be void, for the following actions:a. authorization of the use of the communication primitive; b. decryption of operational data or any part of it; c. performing a command with input data; d. encryption of any operational data resulting from any operation performed; e. computation of a proof of completion of any performed action or of correctness of the resulting data to be used in security computations.', 'a. authorization of the use of the communication primitive;', 'b. decryption of operational data or any part of it;', 'c. performing a command with input data;', 'd. encryption of any operational data resulting from any operation performed;', 'e. computation of a proof of completion of any performed action or of correctness of the resulting data to be used in security computations.', '19. Data exchange system according to claim 17 characterized in that the data processing unit (5) generates a random transaction number upon initializing data transfer, which serves as basis for cryptographic computations.

20. Data exchange system according to claim 17 characterized in that one communication primitive is assigned a specified value which will always be interpreted as a request to enter a new interaction context (19(1) . . . ).

21. Data exchange system according to claim 17 characterized in that it comprises a further data processing unit (4) comprising the same elements as the data processing unit (4) which might optionally contain in its memory an application programmers interface (10) which consists of program code designed to allow additional computer programs to be implemented to give users control over the sequence of exchanged communication primitives or to influence the data transferred in them or to learn or further process the data received in the exchange.

22. Data exchange system according to claim 21 characterized in that the primitive used to enter a specified interaction context (19(1) . . . ) comprises numeric values to be used in security calculations in subsequent communications, a first value generated randomly or of similarly unique nature by one of the processing units and possibly a second value serving to proof the authenticity of said one processing unit or to otherwise identify said one processing unit.

23. Data exchange system according to claim 21 characterized in that each communication primitive except a first one signalling a reset is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a fixed number of binary values each of which is interpreted by the executive program (12, 17) as a reference to a single data element.

24. Data exchange system according to claim 21 characterized in that each communication primitive except a first one signalling a reset is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being used to determine which of the data elements available for external reference in an active interaction context (19(1) . . . ) will be used while performing responding actions in such a way that any data element is selected if it contains a value that matches said second value or if it contains a value that is otherwise sufficient to indicate it.

25. Data exchange system according to claim 21 characterized in that each communication primitive except a first one signalling a reset is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a number of binary values which are assigned specific meanings by the executive program (12, 17) to be used in interpreting data formats in the communication primitive and in performing responding actions.

26. Data exchange system according to claim 17 characterized in that portable processing units are implemented in smart cards.

27. Data exchange system according to claim 17 characterized in that portable processing units are implemented in PCMCIA cards.

28. Data exchange system according to claim 26 characterized in that the communication means (14) utilizes external communication means to establish a data link (6) such external communication means as are made available to the data processing unit (5) by the data processing unit, or similar such electronic device hosting the PCMCIA or smart card which implements the data processing unit (5).

29. Data exchange system according to claim 17 characterized in that the data processing unit (4) is implemented as portable personal computer.', '30. Data exchange system according to claim 28 characterized in that the communication means (7) utilizes a smart card reader.', '31. Data exchange system according to claim 28 characterized in that the communication means (7) utilizes a PCMCIA card slot.', '32. Data exchange system according to claim 26 characterized in that the communication means (7) primarily or additionally utilizes non contact data transfer with electromagnetic fields.']