Andre, Here are my comments on the SAGA strawman API v0.2. I would be very interested to hear your opinions about my comments on the API. I have in-lined the text below as well as attaching the document. Thanks, Graeme -------------------------------------------------------- ######### General comments -1.1 The comments in this document stem from my experiences in producing complete Java language bindings of the API (based upon the strawman API 0.2), and a trivial Java implementation of SAGA.NameSpace, SAGA.File and SAGA.JobManagement packages. Whilst this exercise was reasonable straightforward, the comments in this document indicate numerous points for discussion/clarification. I also expect that implementations of the remaining namespaces (SAGA.LogicalFile, SAGA.Stream and SAGA.Task) would raise additional comments about the API in these areas. I believe that trial implementations will prove the best way to debug this API before the draft is finalised. -1.2 The API is inconsistent between different sections of the document. For example, the interface for Session is defined as a pre-requisite for the creation of all SAGA objects, however this is not referred to in any other part of the API. Similarly strawman_task.txt says that each object in the SAGA API must define a createTaskFactory() method, but this is not included in the SIDL definition. Perhaps there should be an individual with editorial control/responsibility for the entire API? -1.3 I understand that issues relating to multiple return values are being deferred to the language bindings. However since this is an issue for many language I suggest that the effects are minimised by tackling it where appropriate in the language independent specification, for examples see 3.21 and 5.7. ######### Queries -2.1 What is the purpose of NSEntry? This is not documented. -2.2 What is the purpose of Async? This is not documented. -2.3 Are all relative paths relative to the user's home directory? For example, JobDefinition.SAGA_JobCwd is described as being relative to the home directory. Is this the same for physical (and logical) files? ######### Specific comments on the API -3.1 Constructors involving Session objects should be defined for all relevant SAGA classes. These classes should also specify an operation to return a session object (i.e. getSession())? -3.2 There should be a specified exception model for the elements of the SAGA API that are not provided by an implementation. This is described in the introduction of the API. May I suggest the SIDL specification specify all methods that may throw a 'NotImplemented' exception ('NotImplemented' is more consistent stylistically than 'NOT_IMPLEMENTED'). -3.3 There is no close() method defined for the File interface. The user should be able to explicitly release a file. -3.4 There are no exceptions defined for any of the interfaces in the SAGA.JobManagement package. There are numerous possible exceptions during the job submission process (aside from failed jobs), for example if the requirements defined by JobDefinition cannot be met, or bad user-parameters are provided. The SAGA API *MUST* define a basic set of possible job management errors through which the implementation specific exceptions that arise can be rethrown. -3.5 Interfaces extending SAGA.Attribute (i.e. Context, JobDefinition, JobExitStatus, JobInfo, Stream, StreamServer) pre-define attributes of a specific type. However, the SAGA.Attribute class only supports values of type String. At present users will have to cast the values themselves. Should SAGA.Attribute be extended to support attribute values of different types (a complementary/alternative solution is provided by 3.6)? In this case an exception type of IncorrectAttributeType should be defined for the methods setAttribute() and setVectorAttribute() (?). -3.6 It may be appropriate to define attribute specific get/set methods for known attributes of interfaces extending SAGA.Attribute (i.e. Context, JobDefinition, JobExitStatus, JobInfo, Stream, StreamServer). For example JobExitStatus defines three known attributes: SAGA_ExitCode SAGA_Signaled SAGA_Termsig These convenience methods would expose the semantics of interface and would provide a typesafe way to handle these pre-define attributes (which have a specified type). For example; void getExitCode(out integer exitcode); void setExitCode(in integer exitcode); Although perhaps setting values should be protected or handled by the constructor. This approach would also reduce the occurrence of runtime errors resulting from typos in the attribute names (since these would be detected at compile time). I had several of these whilst playing with my toy implementation. -3.7 SAGA.NameSpace.NSDir defines method changeDir(), since the directory can change there should be a method to query the current directory (i.e. pwd()). -3.8 A specific exception should be defined for Multiplexer.watch() -3.9 Could the enumerations be defined as integers in the range 0-MAXVALUE? This makes it simpler to validate the values, for example where contextType is defined as: public final class contextType { public final static int X509 = 0; public final static int MyProxy = 1; public final static int SSH = 2; public final static int Kerberos = 3; public final static int UserPass = 4; public final static int MAXVALUE = 5; } a supplied integer value could be validated with the code: if (type>=0 && type<SAGA.contextType.MAXVALUE) This would require the following enumerations to be altered: File.openFlags, LogicalFile.openFlags, NameSpace.copyFlags, NameSpace.linkFlags, NameSpace.makeDirFlags, NameSpace.moveFlags, NameSpace.removeFlags, Stream.ActivityType. -3.10 "Any SAGA operation can throw a IncorrectSession exception" the SIDL should specify method which may throw this exception. -3.11 All of the exceptions that may be thrown by methods must be specified in the SIDL specification for that method. -3.12 The Session objects should provide some method to allow them to be serialised/deserialised. This would allow the user to submit jobs, quit the application and resume at a later date. At the simplest save() and load() methods could be defined. In the world of Globus 2.4 all that you needed was the GRAM job handle string, whilst this information is resource specific the SAGA API should strive for the same simplicity. For example, imagine the following scenario required to regain control of a job object (please excuse the Java syntax): Session mysession = new Session(args); //Create session with specific arguments JobService js = new JobService(mysession); //Create JobService with config defined by mysession Job myjob = js.runJob( "localhost", "\bin\date" ); //Submit job String myjobid = js.getJobID(); //Get jobID mysession.save("somefile.xml"); //Save the session to file %%% Quit the application, and restart Session mysession = Session.load("somefile.xml"); //Load the session from file JobService js = new JobService(mysession); //Create JobService with original config defined by mysession Job myjob = js.getJob(myjobid); //Create Job object corresponding to my job ... //Do stuff Of course in this example if the JobService had been instantiated without the optional Session argument a default configuration would have been used, and all that would be required to recreate the Job object would be the jobID string. -3.13 Could the Job interface provide the convenience function wait() (or similar, i.e. waitUntilComplete() to prevent confusion with Task.wait())? This would save user effort of scripting a polling function, or similar. This would also be useful in situations where explicit job status is not available until completion, for example when forking a job using java.lang.Runtime you may only call waitFor() on a process (there is no other simple way to determine whether it is complete). -3.14 Methods of SAGA.Attibute throw the NoSuchKey exception if a key is not present (rather than returning null, see 4.6), would it be possible to define a "boolean = hasKey(String key)" method? Actually, it soon got pretty tedious handling NoSuchKey exceptions, perhaps it better for getAttribute() to return null (or perhaps not). -3.15 It is not clear to me how the ErrorHandler interface corresponds to the Java exception handling model. Which errors are intended to be handled via this interface? Any serious errors I will throw immediately, in my trial interface the error handler became the repository for crud exceptions that could otherwise be ignored, which is wasted effort. I suggest that the ErrorHandler interface is redundant in Java because it is supplanted by the natural way to handle exceptions in this language. The ErrorHandler may be appropriate in other languages, however in many cases I would expected there already to be a tried and tested method for dealing with errors. Rather than reinvent the wheel I would remove this section of the API and leave this to the language bindings to handle errors in the manner appropriate for each language. (see 3.20) -3.16 Should NSDir.makeDir() return an object NSdir corresponding to the created directory? -3.17 The replication of the enumerations openDirFlags and openFlags between the packages SAGA.Namespace, SAGA.File and SAGA.LogicalFile is a little confusing. I understand that File and LogicalFile extend\override these enumerations, is there a neat solution to this problem? - Ignore this otherwise. -3.18 How should permission denied exceptions be modelled by SAGA.File.Directory? A new exception type required; 'PermissionDenied'. -3.19 NSDir.list(dir) should return a String array rather than a String. Also would it not be preferable to have a NSDir.list() method to return the contents of the directory? -3.20 I am very dubious about the value of the SAGA.Task API within the context of high-level languages. Where asynchronous method invocation exists, supported either within the language (i.e. delegates in C#) or documented design patterns (i.e. inner classes in Java), I suggest that the semantics of the language should take precedence over the semantics of the SAGA API (this also applies the Exception handling in high-level languages). I am not certain whether asynchronous method invocation should simply be left to the language bindings, or be overridden in the language bindings when accepted solutions already exist. (see 3.15) -3.21 JobService.runJob() returns Job and stdin, stdout, stderr. However stdin, stdout, stderr are available from Job.getJobInfo()? I understand that this is a convenience functions but this is a prime example of the multiple return values problem. Can runJob() simply return an object Job? -3.22 I dislike that capitalisation of namespaces in the API, in particular where the namespace is the same as a class that it contains, for example; SAGA.File.File SAGA.LogicalFile.LogicalFile SAGA.Stream.Stream SAGA.Task.Task This is merely a stylistic point, however it would be clearer is the namespace elements were changed to lowercase, for example; SAGA.file.File ######### Comments on the Strawman API document -4.1 The following methods of File are not documented in strawman_files.txt: void readP (in pattern pattern, out string buffer, out long len_out ); void writeP (in pattern pattern, in string buffer, out long len_out ); void lsEModes (out array<string,1> emodes ); void readE (in string emode, in string spec, out string buffer, out long len_out ); void writeE (in string emode, in string spec, in string buffer, out long len_out ); -4.2 The interface Exception does not need to extend sidl.SIDLException. You do not intend to build language bindings to be built with Babel. -4.3 In the details of Job.signal() signum is incorrectly listed as an output -4.4 The following methods are not described in strawman_namespace.txt: void getURL (out string name ); void getName (out string name ); -4.5 Details of Multiplexer.wait() differs from SIDL spec. -4.6 Details of Attribute.getVectorAttribute() specifies that it will return NULL if key is not present, but also specifies NoSuchKey exception. This should be consistent with the other methods of this class. -4.7 Enumeration values of JobState are not provided -4.8 JobState enumeration values are inconsistently capitalised within the API documentation. For example, DoneOk is referred to as DONE_OK. -4.9 Exceptions are not described in the SIDL interface, however Exception types are listed in long description of the methods (for example ReadOnlyAttribute and NoSuchKey). This information should be in the SIDL description as it is fundamental to the interface. -4.10 Enumerations are inconsistently capitalised. Capitalise ivec, openDirFlags, openFlags? -4.11 LogicalFile argument types not specified for addLocation, removeLocation, replicate. These should be 'string' -4.12 The interfaces Stream and StreamServer implements Attributes, however Attributes does not exist. This should be Attribute (although perhaps Attributes is a better name for this interface)? -4.15 File.readP() and File.writeP() define input argument of type 'pattern'. This type is not defined by the SIDL API. -4.16 In SAGA.Stream.Stream void getContext (out context info); should read void getContext (out Context info); -4.17 strawman_error.txt: "All objects in SAGA implement ErrorHandler...", the SIDL for these objects should indicate that they implement the ErrorHandler interface. The following objects: Directory File Job JobService LogicalDirectory LogicalFile Multiplexer Stream StreamServer Task TaskContainer ... any others ? ######### Comments on Java language bindings -5.1 JobInfo; the Java stream classes InputStream and OutputStream used in place of opaque -5.2 Mapping SAGA exceptions into Java exception model: SAGA.Exception extends java.lang.Exception the constructor would allow the ExceptionCategory to be defined SAGA.Exception(String message, ExceptionCategory category) and other defined Exception types would then subclass SAGA.Exception (at present all exceptions are defined in the root SAGA package, with a little effort they could be categorised throughout the package structure) -5.3 Enumerations are supplied as a class containing constant field values as public static ints. This is the simplest solution, however a typesafe solution could be provided if required. -5.4 The API is defined as a collection of interfaces that may be implemented to provide access to Grid resources. Interfaces are the most suitable solution. However the inability to describe constructors in a Java interface is problematic since constructors are occasionally defined in SIDL specification. There is no way to make implementing classes honour a specific constructor signature, instead the documentation for the interface should suggest constructors that should be provided by any implementing class. -5.5 Implementations could be provided for generic classes to prevent developers from needing to re-implementing, for example; Attribute, Context. Obviously implementation specific subclasses of these would have to be defined as 'abstract' classes. Rather I think that an interface only solution is simpler and more flexible in the long term, default implementations of generic classes could still be provided. -5.6 Single out arguments become the method return type. -5.7 Mutiple out arguments must be worked around (hopefully there will be as few as possible in the API). For example, in defining the interface for the File class the following method: void read (in long len_in, out string buffer, out long len_out ); became: java.lang.String read(long len_in) since it is straightforward to determine the length of a String. -5.8 Relative paths are relative to user's home directory, they should not be relative to the elusive Java current working directory. Therefore it is necessary to perform a mapping using java.io.File objects (see the article 'Java Applications and the "Current Directory"' http://www.devx.com/tips/Tip/13804). ######### General comments -1.1 The comments in this document stem from my experiences in producing complete Java language bindings of the API (based upon the strawman API 0.2), and a trivial Java implementation of SAGA.NameSpace, SAGA.File and SAGA.JobManagement packages. Whilst this exercise was reasonable straightforward, the comments in this document indicate numerous points for discussion/clarification. I also expect that implementations of the remaining namespaces (SAGA.LogicalFile, SAGA.Stream and SAGA.Task) would raise additional comments about the API in these areas. I believe that trial implementations will prove the best way to debug this API before the draft is finalised. -1.2 The API is inconsistent between different sections of the document. For example, the interface for Session is defined as a pre-requisite for the creation of all SAGA objects, however this is not referred to in any other part of the API. Similarly strawman_task.txt says that each object in the SAGA API must define a createTaskFactory() method, but this is not included in the SIDL definition. Perhaps there should be an individual with editorial control/responsibility for the entire API? -1.3 I understand that issues relating to multiple return values are being deferred to the language bindings. However since this is an issue for many language I suggest that the effects are minimised by tackling it where appropriate in the language independent specification, for examples see 3.21 and 5.7. ######### Queries -2.1 What is the purpose of NSEntry? This is not documented. -2.2 What is the purpose of Async? This is not documented. -2.3 Are all relative paths relative to the user's home directory? For example, JobDefinition.SAGA_JobCwd is described as being relative to the home directory. Is this the same for physical (and logical) files? ######### Specific comments on the API -3.1 Constructors involving Session objects should be defined for all relevant SAGA classes. These classes should also specify an operation to return a session object (i.e. getSession())? -3.2 There should be a specified exception model for the elements of the SAGA API that are not provided by an implementation. This is described in the introduction of the API. May I suggest the SIDL specification specify all methods that may throw a 'NotImplemented' exception ('NotImplemented' is more consistent stylistically than 'NOT_IMPLEMENTED'). -3.3 There is no close() method defined for the File interface. The user should be able to explicitly release a file. -3.4 There are no exceptions defined for any of the interfaces in the SAGA.JobManagement package. There are numerous possible exceptions during the job submission process (aside from failed jobs), for example if the requirements defined by JobDefinition cannot be met, or bad user-parameters are provided. The SAGA API *MUST* define a basic set of possible job management errors through which the implementation specific exceptions that arise can be rethrown. -3.5 Interfaces extending SAGA.Attribute (i.e. Context, JobDefinition, JobExitStatus, JobInfo, Stream, StreamServer) pre-define attributes of a specific type. However, the SAGA.Attribute class only supports values of type String. At present users will have to cast the values themselves. Should SAGA.Attribute be extended to support attribute values of different types (a complementary/alternative solution is provided by 3.6)? In this case an exception type of IncorrectAttributeType should be defined for the methods setAttribute() and setVectorAttribute() (?). -3.6 It may be appropriate to define attribute specific get/set methods for known attributes of interfaces extending SAGA.Attribute (i.e. Context, JobDefinition, JobExitStatus, JobInfo, Stream, StreamServer). For example JobExitStatus defines three known attributes: SAGA_ExitCode SAGA_Signaled SAGA_Termsig These convenience methods would expose the semantics of interface and would provide a typesafe way to handle these pre-define attributes (which have a specified type). For example; void getExitCode(out integer exitcode); void setExitCode(in integer exitcode); Although perhaps setting values should be protected or handled by the constructor. This approach would also reduce the occurrence of runtime errors resulting from typos in the attribute names (since these would be detected at compile time). I had several of these whilst playing with my toy implementation. -3.7 SAGA.NameSpace.NSDir defines method changeDir(), since the directory can change there should be a method to query the current directory (i.e. pwd()). -3.8 A specific exception should be defined for Multiplexer.watch() -3.9 Could the enumerations be defined as integers in the range 0-MAXVALUE? This makes it simpler to validate the values, for example where contextType is defined as: public final class contextType { public final static int X509 = 0; public final static int MyProxy = 1; public final static int SSH = 2; public final static int Kerberos = 3; public final static int UserPass = 4; public final static int MAXVALUE = 5; } a supplied integer value could be validated with the code: if (type>=0 && type<SAGA.contextType.MAXVALUE) This would require the following enumerations to be altered: File.openFlags, LogicalFile.openFlags, NameSpace.copyFlags, NameSpace.linkFlags, NameSpace.makeDirFlags, NameSpace.moveFlags, NameSpace.removeFlags, Stream.ActivityType. -3.10 "Any SAGA operation can throw a IncorrectSession exception" the SIDL should specify method which may throw this exception. -3.11 All of the exceptions that may be thrown by methods must be specified in the SIDL specification for that method. -3.12 The Session objects should provide some method to allow them to be serialised/deserialised. This would allow the user to submit jobs, quit the application and resume at a later date. At the simplest save() and load() methods could be defined. In the world of Globus 2.4 all that you needed was the GRAM job handle string, whilst this information is resource specific the SAGA API should strive for the same simplicity. For example, imagine the following scenario required to regain control of a job object (please excuse the Java syntax): Session mysession = new Session(args); //Create session with specific arguments JobService js = new JobService(mysession); //Create JobService with config defined by mysession Job myjob = js.runJob( "localhost", "\bin\date" ); //Submit job String myjobid = js.getJobID(); //Get jobID mysession.save("somefile.xml"); //Save the session to file %%% Quit the application, and restart Session mysession = Session.load("somefile.xml"); //Load the session from file JobService js = new JobService(mysession); //Create JobService with original config defined by mysession Job myjob = js.getJob(myjobid); //Create Job object corresponding to my job ... //Do stuff Of course in this example if the JobService had been instantiated without the optional Session argument a default configuration would have been used, and all that would be required to recreate the Job object would be the jobID string. -3.13 Could the Job interface provide the convenience function wait() (or similar, i.e. waitUntilComplete() to prevent confusion with Task.wait())? This would save user effort of scripting a polling function, or similar. This would also be useful in situations where explicit job status is not available until completion, for example when forking a job using java.lang.Runtime you may only call waitFor() on a process (there is no other simple way to determine whether it is complete). -3.14 Methods of SAGA.Attibute throw the NoSuchKey exception if a key is not present (rather than returning null, see 4.6), would it be possible to define a "boolean = hasKey(String key)" method? Actually, it soon got pretty tedious handling NoSuchKey exceptions, perhaps it better for getAttribute() to return null (or perhaps not). -3.15 It is not clear to me how the ErrorHandler interface corresponds to the Java exception handling model. Which errors are intended to be handled via this interface? Any serious errors I will throw immediately, in my trial interface the error handler became the repository for crud exceptions that could otherwise be ignored, which is wasted effort. I suggest that the ErrorHandler interface is redundant in Java because it is supplanted by the natural way to handle exceptions in this language. The ErrorHandler may be appropriate in other languages, however in many cases I would expected there already to be a tried and tested method for dealing with errors. Rather than reinvent the wheel I would remove this section of the API and leave this to the language bindings to handle errors in the manner appropriate for each language. (see 3.20) -3.16 Should NSDir.makeDir() return an object NSdir corresponding to the created directory? -3.17 The replication of the enumerations openDirFlags and openFlags between the packages SAGA.Namespace, SAGA.File and SAGA.LogicalFile is a little confusing. I understand that File and LogicalFile extend\override these enumerations, is there a neat solution to this problem? - Ignore this otherwise. -3.18 How should permission denied exceptions be modelled by SAGA.File.Directory? A new exception type required; 'PermissionDenied'. -3.19 NSDir.list(dir) should return a String array rather than a String. Also would it not be preferable to have a NSDir.list() method to return the contents of the directory? -3.20 I am very dubious about the value of the SAGA.Task API within the context of high-level languages. Where asynchronous method invocation exists, supported either within the language (i.e. delegates in C#) or documented design patterns (i.e. inner classes in Java), I suggest that the semantics of the language should take precedence over the semantics of the SAGA API (this also applies the Exception handling in high-level languages). I am not certain whether asynchronous method invocation should simply be left to the language bindings, or be overridden in the language bindings when accepted solutions already exist. (see 3.15) -3.21 JobService.runJob() returns Job and stdin, stdout, stderr. However stdin, stdout, stderr are available from Job.getJobInfo()? I understand that this is a convenience functions but this is a prime example of the multiple return values problem. Can runJob() simply return an object Job? -3.22 I dislike that capitalisation of namespaces in the API, in particular where the namespace is the same as a class that it contains, for example; SAGA.File.File SAGA.LogicalFile.LogicalFile SAGA.Stream.Stream SAGA.Task.Task This is merely a stylistic point, however it would be clearer is the namespace elements were changed to lowercase, for example; SAGA.file.File ######### Comments on the Strawman API document -4.1 The following methods of File are not documented in strawman_files.txt: void readP (in pattern pattern, out string buffer, out long len_out ); void writeP (in pattern pattern, in string buffer, out long len_out ); void lsEModes (out array<string,1> emodes ); void readE (in string emode, in string spec, out string buffer, out long len_out ); void writeE (in string emode, in string spec, in string buffer, out long len_out ); -4.2 The interface Exception does not need to extend sidl.SIDLException. You do not intend to build language bindings to be built with Babel. -4.3 In the details of Job.signal() signum is incorrectly listed as an output -4.4 The following methods are not described in strawman_namespace.txt: void getURL (out string name ); void getName (out string name ); -4.5 Details of Multiplexer.wait() differs from SIDL spec. -4.6 Details of Attribute.getVectorAttribute() specifies that it will return NULL if key is not present, but also specifies NoSuchKey exception. This should be consistent with the other methods of this class. -4.7 Enumeration values of JobState are not provided -4.8 JobState enumeration values are inconsistently capitalised within the API documentation. For example, DoneOk is referred to as DONE_OK. -4.9 Exceptions are not described in the SIDL interface, however Exception types are listed in long description of the methods (for example ReadOnlyAttribute and NoSuchKey). This information should be in the SIDL description as it is fundamental to the interface. -4.10 Enumerations are inconsistently capitalised. Capitalise ivec, openDirFlags, openFlags? -4.11 LogicalFile argument types not specified for addLocation, removeLocation, replicate. These should be 'string' -4.12 The interfaces Stream and StreamServer implements Attributes, however Attributes does not exist. This should be Attribute (although perhaps Attributes is a better name for this interface)? -4.15 File.readP() and File.writeP() define input argument of type 'pattern'. This type is not defined by the SIDL API. -4.16 In SAGA.Stream.Stream     void getContext (out context info);   should read     void getContext (out Context info); -4.17 strawman_error.txt: "All objects in SAGA implement ErrorHandler...", the SIDL for these objects should indicate that they implement the ErrorHandler interface. The following objects:     Directory     File     Job     JobService     LogicalDirectory     LogicalFile     Multiplexer     Stream     StreamServer     Task     TaskContainer     ... any others ? ######### Comments on Java language bindings -5.1 JobInfo; the Java stream classes InputStream and OutputStream used in place of opaque -5.2 Mapping SAGA exceptions into Java exception model: SAGA.Exception extends java.lang.Exception the constructor would allow the ExceptionCategory to be defined SAGA.Exception(String message, ExceptionCategory category) and other defined Exception types would then subclass SAGA.Exception (at present all exceptions are defined in the root SAGA package, with a little effort they could be categorised throughout the package structure) -5.3 Enumerations are supplied as a class containing constant field values as public static ints. This is the simplest solution, however a typesafe solution could be provided if required. -5.4 The API is defined as a collection of interfaces that may be implemented to provide access to Grid resources. Interfaces are the most suitable solution. However the inability to describe constructors in a Java interface is problematic since constructors are occasionally defined in SIDL specification. There is no way to make implementing classes honour a specific constructor signature, instead the documentation for the interface should suggest constructors that should be provided by any implementing class. -5.5 Implementations could be provided for generic classes to prevent developers from needing to re-implementing, for example; Attribute, Context. Obviously implementation specific subclasses of these would have to be defined as 'abstract' classes. Rather I think that an interface only solution is simpler and more flexible in the long term, default implementations of generic classes could still be provided. -5.6 Single out arguments become the method return type. -5.7 Mutiple out arguments must be worked around (hopefully there will be as few as possible in the API). For example, in defining the interface for the File class the following method: void read (in long len_in, out string buffer, out long len_out ); became: java.lang.String read(long len_in) since it is straightforward to determine the length of a String. -5.8 Relative paths are relative to user's home directory, they should not be relative to the elusive Java current working directory. Therefore it is necessary to perform a mapping using java.io.File objects (see the article 'Java Applications and the "Current Directory"' http://www.devx.com/tips/Tip/13804).