SOPHYA persistence

Figure 1: partial class diagram for classes handling persistence in Sophya

A simple persistence mechanism is defined in SOPHYA. Its main features are:

Portable file format, containing the description of the data structures and object hierarchy.
PPF Portable Persistence file Format.

Handling of read/write for multiply referenced objects.

All write operations are carried using sequential access only. This holds also for read operations, unless positional tags are used. SOPHYA persistence services can thus be used to transfer objects through network links.

The serialisation (reading/writing) for objects for a given class is implemented through a handler object. The handler class inherits from PPersist class.

A run time registration mechanism is used in conjunction with RTTI (Run Time Type Identification) for identifying handler classes when reading PInPersist streams, or for associating handlers with data objects AnyDataObject for write operations.

A complete description of SOPHYA persistence mechanism and guidelines for writing delegate classes for handling object persistence is beyond the scope of this document. The most useful methods for using Sophya persistence are listed below:

POutPersist::PutObject(AnyDataObj & o)
Writes the data object o to the output stream.

POutPersist::PutObject(AnyDataObj & o, string tagname)
Writes the data object o to the output stream, associated with an identification tag tagname.

PInPersist::GetObject(AnyDataObj & o)
Reads the next object in stream into o. An exception is generated for incompatible object types.

PInPersist::GetObject(AnyDataObj & o, string tagname)
Reads the object associated with the tag tagname into o. An exception is generated for incompatible object types.

The operators operator << (POutPersist ...) and operator >> (PInPersist ...) are often overloaded to perform PutObject() and GetObject() operations, as illustrated in the example below:

// Creating and filling a histogram
Histo hw(0.,10.,100);
...
// Writing histogram to a PPF stream
POutPersist os("hw.ppf");
os << hw;
// Reading a histogram from a PPF stream
PInPersist is("hr.ppf");
is >> hr;

The scanppf program can be used to list the content of a PPF file.

csh> scanppf -h
SOPHYA Version  1.1 Revision 0 (V_Fev2001) -- Feb 28 2001 11:19:17 cxx
 Usage: scanppf filename [s/n/a0/a1/a2/a3]
   s[=default} : Sequential reading of objects
   n : Object reading at NameTags
   a0...a3 : Tag List with PInPersist.AnalyseTags(0...3)