T 0912/10 (Process attachable virtual machine/SAP) 30-06-2014

1. Overview

1.1 The application as claimed relates to isolating user sessions in a server. The server runs for example Java servlets or Enterprise Java Beans (EJBs) in a virtual machine (VM; page 1, lines 9-18; see also the priority appli­ca­tion P2, page 1, paragraph 3). According to the board's under­standing, a user session can be thought as a series of related http requests of the same user who operates on his client computer a browser program which sends these http requests calling a Java servlet or a function of an EJB on the server.

Typically, a large number of user sessions is running within a single VM (page 1, lines 16-18; P2, page 1, paragraph 4). This makes isolation of the user sessions difficult. In the application, each user session is provided with its own VM (page 2, lines 5-6; P2, page 1, paragraph 6), a so-called "process attachable virtual machine" (PAVM) which can be attached to and detached from the process in which it is executed (page 7, para­graph 1; P2, page 1, para­graph 6). When a user session starts, its corresponding PAVM is created and a memory area (called "session memory" in the descrip­tion) is allocated in shared memory. This session memory stores the PAVM, the PAVM context (stack and heap) and the context of the user session (called "user context" in the claims; page 9, paragraph 2; figure 4; first step of initia­lizing/creating a PAVM and allocating the session memory in claim 1 of all requests; P2, page 1, para­graph 8). The user context consists of a user stack and a user heap (claims 4, 7 of the main request; original claims 7, 11; page 14, paragraphs 3 and 4), and is included in the PAVM context in the case of a Java VM (page 8, paragraph 3; P2, page 11, paragraph 2 and page 15, section 5.1.2).

A pool of special OS processes (called "work pro­ces­ses") exists in the server to allow a PAVM to run in one of the processes in order to serve a request of the corresponding user session (page 2, lines 6-12; page 7, paragraph 2; P2, page 1, para­graph 6). This means, when a user session sends a request to the server, the PAVM corresponding to the user session is attached or bound to one of the available processes, and then can be detached from said process after the request has been served by the PAVM (page 15, paragraph 3; P2, page 1, para­graph 3, last line: "thread pool based archi­tec­ture" and page 11, line 3: "process pool archi­tec­ture"). To achieve this, the computational state of the PAVM needs to be persisted, when the PAVM is detached from a process, and unpersisted when the PAVM is (re-)attached to a process (page 8, para­graph 2; P2, page 1, para­graph 7). Through the use of shared memory, persisting and unpersisting become low cost operations (page 8, lines 10-13; page 9, lines 12-14; page 15, lines 16-19; page 16, lines 5-7; P2, page 1, para­graph 8): The PAVM's session memory simply has to be mapped to/unmapped from the address space of the process; no data is actually moved or copied (page 9, lines 13-16; P2, page 1, para­graph 8). By mapping only one session memory into a process at a time, the user sessions are fully isolated (page 13, paragraph 3; page 5, para­graph 4; not claimed in the main request and the second auxiliary request; P2, page 1, para­graph 14). The description (page 15, lines 19-23; page 16, lines 7-11) also mentions an alternative persisting/unper­sisting method, namely to/from files which is much slower and more complicated than using shared memory. This is missing in the priority appli­cation P2.

To summarise, a one-to-one correspondence between a user session and its PAVM is kept during the lifetime of a user session, whereas the process in which the PAVM is executed may change from request to request of that user session. The isolation between the user sessions is achieved through this one-to-one correspondence (page 7, first paragraph; P2, page 1, para­graph 6) and through a separate session memory for each user session (page 9, paragraph 2; P2, page 1, para­graph 8).

1.2 The board judges that all three requests are in respect of the same invention (Article 87(1) EPC) as priority applica­tion P2.

1.3 Claim 1 of the first auxiliary request satisfies the requirements of Article 123(2) EPC. This was denied in the appealed decision with respect to corresponding claim 1 of the then second auxiliary request.

2. Priority

2.1 Main request

2.1.1 According to the appealed decision (3.3, last para­graph) as it concerns the validity of the priority of appli­cation P2 for the refused main request (whose claims correspond to the current main request in appeal), P2 does not disclose that the feature of "mapping" is optional for the subject-matter of P2. It only discloses "binding" in combination with "mapping".

2.1.2 According to the grounds of appeal (page 10, para­graph 3), P2 discloses "attaching" (= "binding") without "mapping" on page 1, paragraph 6, last sentence: "User requests are dispatched to work processes, which attach the appropriate PAVM and have it process the request". According to paragraph 4 of the grounds, there is another explicit disclosure of "binding" without "mapping" in P2, namely in claims 1, 2 and 5 on page 30.

2.1.3 According to the decision (3.6), P2 consists of 5 separate documents and it is inadmissible to combine features form the first and the last part of P2, i.e. from pages 1 and 2 on the one hand and from claims 1, 2 and 5 on page 30 on the other hand. The features of the two parts are different.

2.1.4 The board agrees with the grounds that at least the second passage in P2 (i.e. claims 1, 2, 5 on page 30) explicitly discloses "binding", "detaching" (i.e. un­binding) and "(re-)binding" without "mapping". These claims do not even (at least explicitly) contain the features of unpersisting and persisting the state of the PAVM, in contrast to claim 1 of the present main request. It is only claimed that, after its creation, the PAVM is stored. Thus, P2 even discloses the invention in a more general way than the present claims. Furthermore, the board cannot see why pages 1 and 2 on the one hand and page 30 on the other hand should represent separate embodiments. The skilled person would understand that the two parts relate to the same invention, but on a different level of detail.

2.1.5 As to the question whether "mapping" is essential (see decision 3.4; grounds, pages 8-13), the board agrees with the grounds (page 11, para­graph 3) that improving the robustness and scalability of server with virtual machines might be taken as the (subjective) technical problem. To solve this problem, the pool of processes and the one-to-one correspondence between user sessions and PAVS seems to be essential. The "mapping", on the other hand,is not. It merely adds another technical effect to the invention, namely that of efficient persisting/unpersisting. The decision seems to restrict the invention to that technical effect. The board considers this to be inappropriate.

2.1.6 In order to check the above reasoning, the board proposes the following thought experiment: suppose an application were filed with P2 as the description and the claims of page 30 of P2 as original claims. If the claims of the main request were filed as amendments would they violate Article 123(2) EPC? The board judges that they would not, since claim 1 of the main request has more details than claim 1 of page 30, and it is not disputed that each of these details is disclosed in what would be the original description (i.e. in P2). For example, claim 1 additionally contains allocating a memory area from shared memory, persisting the state of the PAVM during detaching and unper­sisting during binding. Moreover the specific combination of features specified in the claim would not add any technical teaching not already contained in P2. According to the board's understanding of the enlarged board's of appeal decision G1/03, it follows that if claim 1 would comply with Article 123(2) when taking P2 as its description, then the application can validly claim priority from P2 for this claim.

2.1.7 The fact that P2 (page 1, paragraphs 7, 8) only discloses one embodiment of persisting/unpersisting, namely by unmapping/mapping shared memory, and that the description (page 15, lines 19-23; page 16, lines 7-11) explicitly discloses a second embodiment, namely by storing to/loading from a file, does not change the scale of possible implementations covered by the features of persisting/unpersisting in claim 1, since the board considers that storing to a file is a straightforward implementation of persisting which would be known to the skilled person as part of the common general knowledge in the art. Indeed the word persisting might be regarded as slightly misleading if one did not know the whole context of the application, since it usually means "storing to a file". In this context however, it means "storing until the end of a user session". This can be achieved either by storing in (shared) memory or by storing in a file.

2.1.8 Thus, the priority of P2 is valid for the claims of the main request.

2.2 First and second auxiliary request

Since claim 1 of these requests contain the feature of "mapping", the priority of P2 is also valid for them.

2.3 Consequently, D1 does not belong to the prior art for any of the present requests and the novelty/inventive step objections over D1 raised in the decision are invalid.

3. Original disclosure of the first auxiliary request

3.1 According to the appealed decision (7.2), the last feature "detaching ... wherein only a single process attachable virtual machine at a time is mapped to the work process" of claim 1 of the then second auxiliary request (corresponding to claim 1 of the first auxiliary request in appeal) is not originally disclosed, since it implies "that unmapping takes place at some point between the start of the operation of detaching and the moment that another PAVM is attached to the work process". However, the application as filed only discloses "that unmapping takes place as part of the operation of detaching, i.e. between the start of the operation of detaching and the end of the operation of detaching".

3.2 The board supposes that the objection relates to the second part of the feature ("wherein ..."), since the first part also appears in the main request and is not objected to in the decision with respect to the main request.

3.3 The board cannot see a contradiction in the above cited two statements of the decision: It seems to be correct that the session memory is unmapped before another PAVM is bound/attached to a work process in order to guaran­tee that only one PAVM at at time is bound/attached to a work process. It is also correct to say that unmap­ping takes place as part of the operation of detaching, since the description (page 9, lines 14-16) states that

"the process of detaching the PAVM from the OS process simply requires unmapping the PAVM's session memory from the address space of the OS process.".

3.4 However, there is no indication anywhere in the appli­cation of the duration of the "operation of de­taching". The board considers that the operation of detaching is essentially functionally defined by the description, so that the "end of the operation of detaching" would be understood by the skilled person to be after the unmapping has happened, inde­pendently of when the unmapping happens (immediately after the detaching from a certain work process or just before binding another PAVM to that work process; the latter is what the decision calls "lazy unmapping" on page 11, para­graph 2). With this definition, there is no contra­diction between the two statements.

Note that if unmapping is deferred until shortly before re-binding the work process to another PAVM ("lazy unmapping"), then also detaching is deferred (one could say "lazy detaching" in analogy). Moreover the board also reads P2 as allowing "lazy detaching" (including "lazy unmapping"), since there is also no indication of the point in time when the detaching takes place.

3.5 Furthermore, the board considers the two passages in the original description (page 4, lines 22, 23 and page 13, lines 17-19) as directly and unambi­guous­ly disclosing the second part of the feature ("where­in ..."). It cannot see any reason why this part should not be added to the first part of the feature, even though the decision (7.3, last para­graph) states that these passages could not be added to an embodiment not having the unmapping feature.

The board agrees with this statement as it stands, but is of the opinion that detaching implicitly includes unmapping (because of the above description passage stating that detaching is achieved by unmapping). Thus, the embodiment contains unmapping and the feature of mapping only one single PAVM at a time can be added.

3.6 Therefore, claim 1 of this request complies with Article 123(2) EPC.

4. Remittal

4.1 The decision under appeal mainly discussed the validity of the priority and examined novelty and inventive step only with respect to document D1 which constituted prior art as a consequence of the denied priority of P2.

4.2 Since the examining division has not yet the opportu­nity to determine the closest prior art on the basis of a valid priority of P2, and therefore also has not yet examined novelty and inventive step of the present claims with respect to such a closest prior art, the board remits the case to the first instance for further prose­cution.