If it's an option, I would use REST for reading from Sage X3. Many entities are already available (everything that's under the "Read-only pages" menu). See below a couple of examples for the Postman calls:

http://YourServer:YourPort/sdata/x3/erp/YourX3Endpoint/BPCUSTOMER('AU001')?representation=BPCUSTOMER.$details

http://YourServer:YourPort/sdata/x3/erp/YourX3Endpoint/BPCUSTOMER?representation=BPCUSTOMER.$query&count=20

(just change BPCUSTOMER for ITMMASTER in your case, and AU001 for the product code you want to see).

For importing data into Sage X3, I would use the Import/Export SOAP web service, as described here:

https://developer.sage.com/api/x3/import-export-guide/developing-with-web-services/

I already used REST web services, i use both of them Combined REST and SOAP but i still confused about the structure and relations, cause as you see in REST there is nothing called GRP but in SOAP if you want to post or export you should use GRP  and also export return a file which is not good pactice for developpement purposes also it returns data seperated by ";" which you can't know every single data is related to what field exactly,in general for posting in soap you need to know every field is related to which GRP. and if i am gonna use SOAP i can't make a great structure to save it in my external db 

I think I understand your issue a little better: SOAP and REST calls are completely different in X3. The format of each can't be used in the other. Additionally, the pre-defined REST calls in X3 are read-only, which means you won't be able to create records in X3 using REST unless you build something custom.

yes exactly, so is there a solution? 

Hi,

I don't think it's necessary to use the GRP names in order to create or save a record.
I just checked creating a product using the ITM web service object, and I created a product just using the following parameters:

<PARAM>
<FLD NAME="TCLCOD">BMSOL</FLD>
<FLD NAME="ITMSTA">1</FLD>
<FLD NAME="DES1AXX">Flat Top Table</FLD>
<FLD NAME="DES2AXX">Poly Top Flat Top Table</FLD>
</PARAM>

Hi,

I don't think it's necessary to use the GRP names in order to create or save a record.
I just checked creating a product using the ITM web service object, and I created a product just using the following parameters:

<PARAM>
<FLD NAME="TCLCOD">BMSOL</FLD>
<FLD NAME="ITMSTA">1</FLD>
<FLD NAME="DES1AXX">Flat Top Table</FLD>
<FLD NAME="DES2AXX">Poly Top Flat Top Table</FLD>
</PARAM>

@Alex Lamarca yes , but there is some tables which impose it like SOH to create command:

 <PARAM>
<FLD NAME="BPCORD">FR001</FLD>
<FLD NAME="SALFCY">FR011</FLD>
<TAB ID="SOH4_1" SIZE="1">
<LIN NUM="1">
<FLD NAME="ITMREF">DIS009</FLD>
<FLD NAME="QTY">2</FLD>
</LIN>
</TAB>
</PARAM>

@Michael C. Bell yes i think so, thank you for your help