## 4 Case Study Analysis and Results
### Blockchain and Decentralisation  
The blockchain is a shared and immutable database. It is defined as a digital register whose transactions are grouped into blocks, linked in chronological order, and cryptography guarantees its integrity [32]. The current size of blockchain networks is still limited but destined to grow over time. Therefore, the blockchain is comparable to a distributed database managed by a network of nodes (computers), each of which has a private copy containing identical information. Generally, the involved nodes do not know each other's identity. A shared protocol allows new blocks to be added to the \"chain\" to ensure consistency between the various copies. Each time a new block is approved-chained (consent), all nodes update their private copy. This structure ensures that no manipulation, modification or deletion of data is possible [16].  
Thanks to the characteristics mentioned above, the blockchain can be conceptually compared to databases and registers managed centrally by recognised and regulated authorities (public administrations, banks, insurance companies, payment intermediaries, etc.), whose fundamental difference consists in being decentralised and immutable, thus representing a valuable alternative in terms of safety, reliability and costs [109].  
A decentralised network (see Figure 3) can be considered the most suitable for integrating the existing ERP systems with a blockchain-based accounting shared ledger [28].  
Accounting information systems (AISs) [SAP FI module] and e-procurement modules [SAP brand new module to be implemented] are expected to play the most crucial role in this integration process. Accounting information systems should include additional bookkeeping processes (i.e., hash axis and shared ledger). In contrast, e-procurement ensures digital signature processes, smart contract management and approval, becoming a critical joining link between centralised ERP system and decentralised business network (see Figures 4 and 5).  
Figure 4: AIS and e-Procurement Processes Combination.  
Figure 3: Decentralised Business Systems Network.  
Smart contracts are often considered an essential part of advanced blockchain architectures since they can secure, facilitate and automate the effects agreed by companies and individuals that signed the contracts [110]. Smart contracts are programmed and stored on a blockchain and automatically execute when prearranged conditions are met without the need for any intermediary or further confirmation [33; 34]. However, smart contracts approvals require digital signatures (preferably using smart cards, digital signature tokens, biometric devices) from individuals entitled to bind the entities that are part of the agreement [111]. Therefore, big companies should delegate this procurement step to ad hoc e-procurement departments, especially when the number of contracts to be signed is high. Furthermore, a specific e-procurement module (also in SAP) is highly advisable to (a) coordinate and possibly automate the smart contracts' management, (b) bridge the accounting transactions with an external shared ledger, and (c) ensure accountability, timely and smooth electronic signature processing.