Hi Giannis,
I guess you refer to ecoinvent - in ecoinvent, the market processes are just mix processes, plus transport effort. You see that input in a market process are products from specific production, according to a modeled market share. These specific production processes link to their production supply chain, and thus this is considered when you include the entire supply chain.
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Does this mean that I must put both the production process and market process for a flow If I want to calculate from cradle to gate and then transporation?
(you guessed maybe now:) no. Use either the market process (for a generic production) or a specific production process. The market process includes the entire transport effort, the specific production process does not, so you will need to add transportation if you go for the specific production.
Best wishes,
Andreas