# A Knowledge Graph Framework to Support Life Cycle Assessment for Sustainable Decision-Making
## 2 Theoretical Foundations and Related Works  
### Life-Cycle Assessments  
LCAs are performed to quantify the potential environmental impacts of products, services, or companies throughout their entire life cycle [4].  
The process of conducting an LCA in general is guided by the ISO 14040:2006 [5] and ISO 14044:2006 [6] standards, which involve four phases: Goal and Scope Definition, Life Cycle Inventory (LCI), Life Cycle Impact Assessment (LCIA), and Interpretation, as illustrated in Figure 1[5,6].  
The Definition of Goal and Scope sets out the framework and objectives for the study, ensuring that they are in line with the intended purpose [7]. It sets the foundation for the methods and boundaries used throughout the LCA.  
During the LCI stage, the compilation of inputs and outputs for the product or process is performed. This compilation encompasses data from the entire life cycle of the product or process, covering stages such as raw material acquisition, manufacturing, utilization, and disposal [8]. To maintain consistency and transparency, this compilation must align with the predefined objectives and scope. In the LCIA stage, the potential environmental impacts associated with the inventory's inputs and outputs are assessed through characterization and evaluation. This assessment utilizes various standardized impact categories and indicators, facilitating the uniform and clear quantification and comparison of climate change impacts across different products or processes. In the Interpretation phase, the findings from the LCI and LCIA are scrutinized to derive conclusions and recommendations and convey those findings to stakeholders. The Interpretation phase is pivotal in supporting informed decision-making and pinpointing opportunities to enhance environmental performance and guide future research [9].  
LCAs can be approached in different ways, each with its own focus and scope. Two dominant methodologies have emerged in both the academic literature and industry practices: attributional life cycle assessment (ALCA) and consequential life cycle assessment (CLCA). ALCA assigns an environmental impact share to all stages of a product's life cycle, ensuring that all processes linked via energy or physical flows are included [10; 11; 12]. This approach models the life cycle based on a static technosphere, where the boundaries and technologies of the system are assumed to remain constant over time [13]. ALCA requires specific modeling constraints to ensure accuracy, such as avoiding double counting and appropriately partitioning multifunctional processes. This partitioning is particularly crucial during the impact assessment phase to correctly allocate environmental burdens  
Figure 1: The four phases of life cycle assessment.  
among co-products or shared processes. CLCA, on the other hand, examines the environmental outcomes resulting from changes in demand or supply, such as the impact of an increase in product demand [14]. CLCA is more flexible and dynamic in its modeling, accounting for how changes in one part of the system can cause ripple effects throughout the economy. It allows for various methods of assessing co-products, including system expansion, substitution, or even factoring in added consumption [15; 16]. Consequently, the foundation of CLCA is characterized by a dynamic technosphere, acknowledging that technologies and market conditions can change in response to decisions [13]. For the purposes of this research, the focus will be on an ALCA. ALCA provides a comprehensive baseline understanding of the environmental impact of a product under current conditions. It aligns with existing regulatory standards and offers a practical approach to assessing environmental impacts. By establishing a detailed inventory of all relevant inputs and outputs associated with a product, ALCA facilitates the identification of key areas where environmental improvements can be made.