# A Knowledge Graph Framework to Support Life Cycle Assessment for Sustainable Decision-Making
## 4 Case Study: 3D Printing
### KG Application: Cypher Queries
#### 4.8.2 Environmental Impact Assessment  
To assess the environmental impact associated with the product's life cycle, we calculated the total CO2 emissions by aggregating the emissions from material use, energy consumption, and transportation. The calculations mentioned are executed by the query illustrated in Listing 6. This query calculates CO2 emissions across the product life cycle by focusing on three main sources of emissions: materials, energy, and transportation. Material emissions are computed by multiplying the quantity of material used (um.amount) by the material's CO2 equivalent per kilogram (m.co2 EquivalentPerKg). For example, in the case of cement (CEM IV 42.5), using 100 kg of material with a CO2 equivalent of 0.688 kg CO2/kg results in 68.8 kg CO2. Energy emissions are calculated by multiplying energy consumption (ce.consumption) by the emissions factor of the energy source (e.co2 EmissionsPerKwh). For example, consuming 100 kWh of electricity with a factor of 0.4 kg CO2/kWh results in 40.0 kg CO2. Transport emissions are derived from the distance traveled (ut.distanceEm) and the greenhouse gas factor of the transport mode (tm.greenhouseGasPerTkm). For a \begin{table}
\begin{tabular}{l l l} \hline
**Product Life Cycle** & **Phase** & **Involved Actors** \\ \hline
3 DP Component A & Production phase & Technician, operator \\
3 DP Component A & Energy production process & Energy manager, technician \\
3 DP Component A & Use phase & User, maintenance engineer \\
3 DP Component A & Disposal phase & Recycling specialist, waste manager \\ \hline
3 DP Prototype B & Design creation & CAD designer, engineer \\
3 DP Prototype B & Pre-processing phase & Material specialist, technician \\
3 DP Prototype B & Post-processing phase & Quality inspector, technician \\ \hline \end{tabular}
\end{table} 
Table 5: Roles involved in each phase of the product life cycle for 3 DP. transport distance of 150 km and a transport mode with a factor of 0.1 kg CO\({}_{2}\)/tkm, the emissions amount to 15.0 kg CO\({}_{2}\). ```
MATCH(plc:ProductLifeCycle{name:\"ProductLifeCycleof3 DP\"})-[: HasPhase]->(phase:Phase), (phase)-[:HasProcess]->(proc:Process) MATCH(proc)-[um:UsesMaterial]->(m:Material) WHEREany(moduleIN$modulesWHEREmoduleINm.module) WITHplc,phase, SUM(um.amount*m.co2 EquivalentPerKg)ASMaterialEmissions MATCH(proc)-[ce:ConsumesEnergy]->(e:EnergySource) WHEREany(moduleIN$modulesWHEREmoduleINe.module) WITHplc,phase,MaterialEmissions, SUM(ce.consumption*e.co2 EmissionsPerKwh)ASEnergyEmissions MATCH(phase)-[:HasTransportProcess]->(tp:TransportProcess)-[ut: UsesTransport]->(tm:TransportMode) WHEREany(moduleIN$modulesWHEREmoduleINtm.module) WITHplc,phase,MaterialEmissions,EnergyEmissions, SUM(ut.distanceKm*tm.greenhouseGasPerTkm/1000)AS TransportEmissions RETURNplc.nameASLifeCycleName, phase.nameASPhaseName, MaterialEmissions, EnergyEmissions, TransportEmissions, MaterialEmissions+EnergyEmissions+TransportEmissionsAS TotalEmissions
```  
**Listing 6** Cypher Query for Calculating Emissions. To ensure flexibility, the query uses dynamic module filtering, allowing emissions to be calculated only for specific stages of the life cycle, such as the extraction of raw materials (A1), transportation (A2) or manufacturing (A3). The dynamic filtering ensures that only emissions corresponding to the selected modules are included. The total emissions are computed by summing material, energy, and transport emissions. These results are illustrated in Table 6, which compares two scenarios involving different types of cement. Scenario 1 uses cement (CEM IV 42.5) with material emissions of 68.8 kg CO\({}_{2}\), energy emissions of 40.0 kg CO\({}_{2}\), and transport emissions of 15.0 kg CO\({}_{2}\), resulting in total emissions of 123.8 kg CO\({}_{2}\). Scenario 2 uses cement (CEM II 42.5) with material emissions of 79.5 kg CO\({}_{2}\), energy emissions of 40.0 kg CO\({}_{2}\), and transport emissions of 10.0 kg CO\({}_{2}\), leading to total emissions of 129.5 kg CO\({}_{2}\).