Nivas,
Once you have extracted the data from database it will give the results (IDATA object).Nextstep will is loop thru results and map the tax values to TAX segment of 850 recordstructure(ST/TAX), like this map rest of the required segments and form an ST segment that contains (eg:BEG,N1,LIN,TAX segments etc…)
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Finally invoke the convertToString and here map the ST segment which i have mentioned above, set the edi 850 schemaname,delimiters following with addICEnvelope(ISA/IEA),addGroupEnvelope(GS/GE) services to generate (Envelope segments) to prepare the valid EDI 850 document (ISA/GS/ST/SE/GE/IEA.
Regarding mapping of addICEnvelope,addGroupEnvelope mapping,refer the WmEDISamples package which will help you with necessary information.
HTH,
#webMethods#Integration-Server-and-ESB#edi