## 3 The Architecture of SLA based Sharing Economy Service  
### SLA Based Sharing Economy Service  
As shown in Figure 1, the proposed sharing economy service consists of four components: Participants, assets, blockchain network, and off-chain data lake. Participants and assets are the basis of the sharing business model. A participant is an actor with unique roles, and for example, they can be the provider of the assets or the user who wants to search and rent assets according to certain conditions automatically. Assets are goods, services, or properties, which can be controlled by electronics locks or access control systems. Assets can represent almost anything in a business network, for example, a vacant house or an idle desktop. To monitor the status of these assets, we can collect various sensor data from sensors that are attached to assets. Participants can perform operations on the blockchain, for example, creating a new asset or exchange assets with other participants. All the interactions between the participants and the blockchain are encrypted with a digital signature to ensure the security of data transmission and the authenticity of the participant's identity. The blockchain network consists of various trusted peers, which hold the smart contract and a copy of the ledger for the network to maintain the data consistency within the network. The smart contract acts as a trusted distributed application that performs business logic running on the blockchain. It can perform either simple operations such as a data update, or complex operation that requires attached conditions. The blockchain preserves a complete up to data history of all transactions, which would follow a lifecycle of a specific asset. The off-chain data lake is an independent data repository, which holds the current values of participants and assets.  
As shown in Figure 2, we insulate the submitting clients from the blockchain network. They are only used to invoke a smart contract and to receive a notification whenever the blockchain network includes a new transaction in the ledger. Participants are members of the business network, with the abilities to have assets and submit transactions. The assets can also invoke smart contracts in the case of sending sensing data collected from them. These data are used to produce a variety of ways for services such as the remote fault diagnosis and maintenance. The participant registry holds the instances of generated participants while the asset registry holds the instances of assets. In this work, we use the enrollment certificates as the mappings of identities to participants, and these certificates are maintained in the identity registry. The blockchain network creates a new mapping to the identity registry whenever the admin bounds an identity to a participant.  
As a consequence, the network can verify the identity in the identity registry when a participant uses that identity to submit transactions. After the identity verification, the participant becomes the current participant who can submit the transaction. The access control in the smart contract manages access to resources by associating a policy. These rules in the blockchain network are applied to the current participant, who performs the authorized operations on resources according to access control requirements.  
Figure 1: Conceptual model of the service level agreement (SLA)-based sharing economy service with the smart contract.  
Figure 2: Proposed sharing economy service interaction diagram.