Existing Access Control Models Research Articles

Access Control for IoT: A Survey of Existing Research, Dynamic Policies and Future Directions.

Internet of Things (IoT) provides a wide range of services in domestic and industrial environments. Access control plays a crucial role in granting access rights to users and devices when an IoT device is connected to a network. However, many challenges exist in designing and implementing an ideal access control solution for the IoT due to the characteristics of the IoT including but not limited to the variety of the IoT devices, the resource constraints on the IoT devices, and the heterogeneous nature of the IoT. This paper conducts a comprehensive survey on access control in the IoT, including access control requirements, authorization architecture, access control models, access control policies, access control research challenges, and future directions. It identifies and summarizes key access control requirements in the IoT. The paper further evaluates the existing access control models to fulfill the access control requirements. Access control decisions are governed by access control policies. The existing approaches on dynamic policies' specification are reviewed. The challenges faced by the existing solutions for policies' specification are highlighted. Finally, the paper presents the research challenges and future directions of access control in the IoT. Due to the variety of IoT applications, there is no one-size-fits-all solution for access control in the IoT. Despite the challenges encountered in designing and implementing the access control in the IoT, it is desired to have an access control solution to meet all the identified requirements to secure the IoT.

УПРАВЛЕНИЕ ДОСТУПОМ К ЭЛЕКТРОННОЙ ИНФОРМАЦИОННО-ОБРАЗОВАТЕЛЬНОЙ СРЕДЕ ВУЗОВ ФЕДЕРАЛЬНЫХ ОРГАНОВ ИСПОЛНИТЕЛЬНОЙ ВЛАСТИ

The purpose of the article: analysis of the problem of ensuring timely authorized access to the resources of the electronic information and educational environment of universities of federal executive authorities and identification of possible directions for its solution. Research methods: system analysis of the problem of ensuring access of officials of universities of federal executive authorities to the resources of the electronic information and educational environment. The result obtained: approaches to improving the existing access control model, optimizing the role-based access scheme and determining unauthorized access attempts based on machine learning methods are proposed. Scope of the proposed approach: access control system of the electronic information and educational environment of universities of federal executive authorities. Scientific novelty: consists in a comprehensive analysis of the problem of creating and functioning of the electronic information and educational environment of universities of federal executive authorities, during which the structure of this environment is determined and its characteristic features are highlighted. Based on the analysis of information security threats in the electronic information and educational environment, the necessity of creating an access control system to its resources, which provides timely authorized access, is substantiated. The proposed approaches to improving the access control system affect not only the improvement of the existing access model by supplementing it with solutions available in the attribute-based access model, but also the optimization of the role- based access scheme using the developed genetic algorithm and the detection of unauthorized access attempts associated with overcoming access rules, based on application of machine learning methods. Experimental results are presented that confirm the effectiveness of the proposed approaches. Contribution: Igor Kotenko – analysis of the state of the art in the creation and application of the electronic information and educational environment of universities of federal executive authorities, setting the task and developing proposals for developing the functionality of the access control system, development of approaches to genetic optimization of the access scheme and detection of unauthorized access attempts using machine learning methods; Igor Saenko – development of approaches to improving the access control system related to the use of an attribute-based access model, genetic optimization of the access scheme and detection of unauthorized access attempts using machine learning methods; Roman Zakharchenko – analysis of technical solutions that ensure the implementation of the access control system to the resources of the electronic information and educational environment of universities of federal executive authorities, Alexander Kapustin – analysis of security threats and access control models to resources of the electronic information and educational environment of universities of federal executive authorities, Mazen Al-Barri – development and experimental study of an approach to detect attempts of unauthorized access to the resources of the electronic information and educational environment of universities of federal executive authorities, based on the use of machine learning methods

Real geo‐time‐based secured access computation model for e‐Health systems

AbstractRole Back Access Control model (RBAC) allows devices to access cloud services after authentication of requests. However, it does not give priority in Big Data to devices located in certain geolocations. Regarding the crisis in a specific region, RBAC did not provide a facility to give priority access to such geolocations. In this paper, we planned to incorporate Location Time‐ (GEOTime) based condition alongside Priority Attribute role‐based access control model (PARBAC), so requesters can be allowed/prevented from access based on their location and time. The priority concept helped to improve the performance of the existing access model. TIME‐PARBAC also ensures service priorities based on geographical condition. For this purpose, the session is encrypted using a secret key. The secret key is created by mapping location, time, speed, acceleration and other information into a unique number, that is, K(Unique_Value) = location, time, speed, accelerator, other information. Spatial entities are used to model objects, user position, and geographically bounded roles. The role is activated based on the position and attributes of the user. To enhance usability and flexibility, we designed a role schema to include the name of the role and the type of role associated with the logical position and the rest of the PARBAC model proposed using official documentation available on the website for Azure internet of things (IoT) Cloud. The implementation results utilizing a health use case signified the importance of geology, time, priority and attribute parameters with supporting features to improve the flexibility of the existing access control model in the IoT Cloud.

Efficient NFS Model for Risk Estimation in a Risk-Based Access Control Model.

Providing a dynamic access control model that uses real-time features to make access decisions for IoT applications is one of the research gaps that many researchers are trying to tackle. This is because existing access control models are built using static and predefined policies that always give the same result in different situations and cannot adapt to changing and unpredicted situations. One of the dynamic models that utilize real-time and contextual features to make access decisions is the risk-based access control model. This model performs a risk analysis on each access request to permit or deny access dynamically based on the estimated risk value. However, the major issue associated with building this model is providing a dynamic, reliable, and accurate risk estimation technique, especially when there is no available dataset to describe risk likelihood and impact. Therefore, this paper proposes a Neuro-Fuzzy System (NFS) model to estimate the security risk value associated with each access request. The proposed NFS model was trained using three learning algorithms: Levenberg–Marquardt (LM), Conjugate Gradient with Fletcher–Reeves (CGF), and Scaled Conjugate Gradient (SCG). The results demonstrated that the LM algorithm is the optimal learning algorithm to implement the NFS model for risk estimation. The results also demonstrated that the proposed NFS model provides a short and efficient processing time, which can provide timeliness risk estimation technique for various IoT applications. The proposed NFS model was evaluated against access control scenarios of a children’s hospital, and the results demonstrated that the proposed model can be applied to provide dynamic and contextual-aware access decisions based on real-time features.

Research on Distributed Dynamic Trusted Access Control Based on Security Subsystem

The flow of data across nodes has become the dominant feature of data sharing in distributed environments with increasingly blurred boundaries, where it is crucial to maintain data access dynamic, trusted, and efficient. However, traditional centralized access control models are not only difficult to apply in distributed environments but also ignore trusted verification of authorized entities. What’s worse, existing access control models rarely consider themselves security, lack independence, at a high risk of being bypassed or tampered with. Thus, we propose in this paper a distributed, dynamic, and trusted access control model, DDTAC-BSS, where the standard Attribute-Based Access Control (ABAC) architecture is modified and extended. To reduce the attack surface, we separate policy enforcement point (PEP) from other core components, they are located in the node system and access control system, respectively. Then, the access control entry point (ACEP) is added as the only interface for the node system to interact with the access control system. Subsequently, the model introduces the entity trusted assessment mechanism to improve the trustworthiness of access control services. Driven by the dynamic attributes, our model can achieve dynamic trusted authorization and fine-grained access control. Moreover, we implement a lightweight, independent, and distributed security subsystem to achieve unified management of policies and decision-making autonomy by message-driven. By considering the independence of the security subsystem, a trusted operating environment is built based on Trusted Execution Environment (TEE) to ensure the security of the access control mechanism itself. The security of our model is proved rigorously based on the non-interference theory. Comprehensive experiments and comparisons have demonstrated the superior functionality, comparable performance, and strong security of our model.

Service-Based Hybrid Access Control Technology with Priority Level for the Internet of Vehicles under the Cloud Architecture

The communication process of devices in IoV under cloud architecture needs to be protected by access control models. However, existing access control models have difficulty establishing the appropriate granularity of permissions in the face of large amounts of data in IoV. Moreover, the access control model may need to temporarily change user privileges to accommodate the dynamic nature of IoV scenarios, a requirement that is difficult to implement for traditional access control models. The unstable connection status of devices in IoV also creates problems for access control. The service (composed of role and attribute) based access control model (in IoV) S-RABAC (V), under the Cloud computing architecture, introduces a formal theoretical model. The model uses attribute grouping and prioritization mechanisms to form a hierarchical structure. The permission combination pattern in the hierarchical structure can avoid duplicate permissions and reduce the number of permissions while ensuring fine-grained permissions. Different layers in the model have different priorities, and when a user’s permission requires temporary changes, it can be adjusted to the corresponding layers according to the user’s priority. In addition, users are allowed to keep their assigned privileges for a period to avoid frequent access control because of unstable connections. We have implemented the proposed access control model in Alibaba Cloud Computing and given six example demonstrations. The experiment shows that this is an access control model that can protect IoV security more effectively. Various unique mechanisms in the model enable S-RABAC(V) to improve the overall access control efficiency. The model adds some extra features compared to ABAC and RBAC and can generate more access control decisions using the priority mechanism.

HEAD Metamodel: Hierarchical, Extensible, Advanced, and Dynamic Access Control Metamodel for Dynamic and Heterogeneous Structures.

The substantial advancements in information technologies have brought unprecedented concepts and challenges to provide solutions and integrate advanced and self-ruling systems in critical and heterogeneous structures. The new generation of networking environments (e.g., the Internet of Things (IoT), cloud computing, etc.) are dynamic and ever-evolving environments. They are composed of various private and public networks, where all resources are distributed and accessed from everywhere. Protecting resources by controlling access to them is a complicated task, especially with the presence of cybercriminals and cyberattacks. What makes this reality also challenging is the diversity and the heterogeneity of access control (AC) models, which are implemented and integrated with a countless number of information systems. The evolution of ubiquitous computing, especially the concept of Industry 4.0 and IoT applications, imposes the need to enhance AC methods since the traditional methods are not able to answer the increasing demand for privacy and security standards. To address this issue, we propose a Hierarchical, Extensible, Advanced, and Dynamic (HEAD) AC metamodel for dynamic and heterogeneous structures that is able to encompass the heterogeneity of the existing AC models. Various AC models can be derived, and different static and dynamic AC policies can be generated using its components. We use Eclipse (xtext) to define the grammar of our AC metamodel. We illustrate our approach with several successful instantiations for various models and hybrid models. Additionally, we provide some examples to show how some of the derived models can be implemented to generate AC policies.

A Review of Blockchain-Based Access Control for the Industrial IoT

The rapid development and wide application of industrial Internet of things (IoT) have made network security issues such as identity authentication, access control, and data privacy more and more important in the distributed network environment, while blockchain technology benefiting from the advantages of decentralization, high confidence, and difficulty tampering are able to solve the trust problem existing in traditional access control technology. In this paper, firstly the basic concepts of access control and blockchain are explained, and the existing access control model and method based on blockchain in the industrial IoT scenario are summarized. Next, according to different implementation methods of blockchain, two technical routes are innovatively divided, i.e., the blockchain acts as a trusted entity (combination blockchain mode) in combination with the traditional access control technology, and the access control model constructed by completely utilizing the brand-new mode (full blockchain mode) of the distributed and non-tampering characteristics of the blockchain. From the angle of these two technical routes, the unique advantages of applying the blockchain to the IoT access control field are analyzed. Then, according to the key issues in the application of blockchain, the current research progress is summarized from the aspects of dynamic access control, space optimization on the chain, privacy data protection, etc. Finally, the further research direction is provided combined with the current challenges of access control mechanism based on industrial IoT.

Efficient decentralized access control for secure data sharing in cloud computing

SummaryAccess control is an important technique in information security that allows legitimate users to gain access to and prevent unauthorized users from getting access to resources in a system. The restriction between access from a user and a shared file of the data owner can be determined by the access policy. In most existing access control models, it is assumed that all entities, including users, the third party, and cloud service provider (CSP), are in the same trust domain. However, in cloud computing environments, it is usually assumed that the CSP cannot be fully trusted, and the data owner (DO) is desired to have the absolute initiative to control data access. This article proposes a blockchain‐based access control scheme for cloud computing, in which the DO maintains an access matrix to describe the access policy. Then, the public keys of all nodes and the access matrix are stored in the blockchain, to ensure the security of the proposed scheme. The DOs can encrypt the large shared files once using a symmetric key in a long time. And they also can encrypt the symmetric key in parallel using the public key of authorized users in a short time. Security analysis proves that the proposed scheme is able to prevent outsourced files from unauthorized access and collusion attack. Experimental results show that the proposed scheme outperforms the existing baselines in terms of overheads on computation and storage. On average, the computation overhead of the proposed scheme is lower than that of the scheme SVPAC, PpBAC, and Timely CP‐ABE by 25.37%, 45.46%, and 36.44%, respectively. The communication overhead of the proposed scheme is lower than that of the scheme Timely CP‐ABE by 17.16%, and it is more secure, although it is higher than that of the scheme SVPAC and PpBAC by 5.88% and 39.05%. And the storage overhead of the proposed scheme is lower than that of the scheme SVPAC, PpBAC, and Timely CP‐ABE by 59.36%, 20.25%, and 61.88%, respectively.

Activity Control Design Principles: Next Generation Access Control for Smart and Collaborative Systems

Traditionally, access control solutions have focused on how to utilize a specific type of decision parameter for access control decisions. While these “decision parameter”-focused approaches have been well accepted, they typically consider access control with centralized administration. Smart and collaborative computing systems (SCSs) such as online social networks, the Internet of Things (IoT) and connected cyber-physical systems (CPSs) require a disparate approach to meet their unique and complex access control requirements primarily because there are multiple participants who create, share, manage and protect resources (e.g., files, smart devices) individually, collaboratively or even competitively. A distinct feature of SCSs is the diffuse nature of control activities and their complex influence on other activities. Activity control (ACON) extends the scope of traditional access control models and considers how multiple administrative authorities (including users) can manage complex and interacting usage, service and control activities. In this paper, we articulate key characteristics and limitations of various existing access control models and highlight the significance and necessity of activity control in smart collaborative ecosystems. We then propose an extended ACON framework for catering to the needs of dynamic SCSs. Furthermore, we compare existing access control design principles and propose a set of activity control design principles for smart and collaborative computing systems. The proposed ACON framework and design principles will provide a solid foundation for secure SCS design and development.

Attribute-Based Access Control for AWS Internet of Things and Secure Industries of the Future

Internet of Things (IoT) is revolutionizing and enhancing the quality of human lives in every aspect. With a disruption of IoT devices and applications, attackers are leveraging weak authentication and access control mechanisms on these IoT devices and applications to gain unauthorized access on user devices and data and cause them harm. Access control is a critical security mechanism to secure the IoT ecosystem which comprises cloud computing and edge computing services along with smart devices. Today major cloud and IoT service providers including Amazon Web Services (AWS), Google Cloud Platform (GCP), and Azure utilize some customized forms of Role-Based Access Control (RBAC) model along with specific authorization policies enabled by policy-based access control models. To enable fine-grained access control and overcome limitations of existing access control models, there is an imminent need to develop a flexible and dynamic access control model for securing smart devices, data and resources in the cloud-enabled IoT architecture. In this paper, we develop a formal attribute-based access control (ABAC) model for AWS IoT by building upon and extending previously developed access control model for AWS IoT, known as AWS-IoTAC model. We demonstrate the applicability of our proposed model through an industrial IoT use case and its implementation in the AWS IoT platform. Our proposed fine grained model for AWS IoT incorporates its existing capabilities and introduces new attributes for IoT entities and attribute-based policies for enabling expressive access control in AWS IoT. We also evaluate the performance of our model on the AWS cloud and IoT platform with the future smart industries use-case to depict the feasibility of our model in a real-world platform.

FairAccess 2.0: a smart contract-based authorization framework for enabling granular access control in IoT

In this paper, we explore access control area as one of the most crucial aspect of security and privacy in IoT. Actually, conventional security and privacy solutions tend to be less tailored for IoT. Then, designing a distributed access control with user-driven approach and privacy-preserving awareness in an IoT environment is of paramount importance. In this direction, we have investigated in our previous work a new way to build a distributed access control framework based on the blockchain technology through our proposed framework, FairAccess. The first version of FairAccess was based on the Bitcoin's UTXO model. However, this version presented limitations in expressing more granular access control policies. To tackle this issue, this paper upgrades the proposed framework to FairAccess2.0 that uses SmartContract concept instead of the locking/unlocking scripts. Thus, we show a possible working implementation based on ABAC policies, deployed on the ethereum blockchain. The obtained results show the efficiency of FairAccess2.0 and its compatibility with a wide range of existing access control models mainly the ABAC model. Finally, a performance and cost evaluation, discussion and future work are elaborated.

FairAccess2.0: a smart contract-based authorisation framework for enabling granular access control in IoT

In this paper, we explore access control area as one of the most crucial aspect of security and privacy in IoT. Actually, conventional security and privacy solutions tend to be less tailored for IoT. Then, designing a distributed access control with user-driven approach and privacy-preserving awareness in an IoT environment is of paramount importance. In this direction, we have investigated in our previous work a new way to build a distributed access control framework based on the blockchain technology through our proposed framework, FairAccess. The first version of FairAccess was based on the Bitcoin's UTXO model. However, this version presented limitations in expressing more granular access control policies. To tackle this issue, this paper upgrades the proposed framework to FairAccess2.0 that uses SmartContract concept instead of the locking/unlocking scripts. Thus, we show a possible working implementation based on ABAC policies, deployed on the ethereum blockchain. The obtained results show the efficiency of FairAccess2.0 and its compatibility with a wide range of existing access control models mainly the ABAC model. Finally, a performance and cost evaluation, discussion and future work are elaborated.

Achieving security scalability and flexibility using Fog-Based Context-Aware Access Control

In the cyberspace environment, access control is one of the foremost fundamental safeguards used to prevent unauthorized access and to minimize the impact from security breaches. Fog computing preserves many benefits for the integration of both internet of things (IoT) and cloud computing platforms. Security in Fog computing environment remains a significant concern among practitioners from academia and industry. The current existing access control models, like the traditional Context-Aware Access Control (CAAC), are limited to access data from centralized sources, and not robust due to lack of semantics and cloud-based service. This major concern has not been addressed in the literature, also literature still lacks a practical solution to control fog data view from multiple sources.This paper critically reviews and investigates the limitations of current fog-based access control. It considers the trade-off between latency and processing overheads which has not been thoroughly studied before. In this paper, a new generation of Fog-Based Context-Aware Access Control (FB-CAAC) framework is proposed to enable flexible access control data from multiple sources. To fill the gap in the literature this paper introduces (i) a general data model and its associated mapping model to collate data from multiple sources. (ii) a data view model to provide an integrated result to the users, dealing with the privacy requirements of the associated stakeholders, (iii) a unified set of CAAC policies with an access controller to reduce both administrative and processing overheads, and (iv) a data ontology to represent the common classes in the relevant data sets. The applicability of FB-CAAC proposal is demonstrated via a walkthrough of the entire mechanism along with several case studies and a prototype testing. The results show the efficiency, flexibility, effectiveness, and practicality of FB-CAAC for data access control in fog computing environment.

Privacy-based medical data protection against internal security threats in heterogeneous Internet of Medical Things

Data and information security is considered to be an important and challenging task for any field of life. But it becomes more critical especially when it deals with the medical field due to life and health hazards. The ratio of internal security threats to external threats always remains high. A huge number of efforts and technical expertise are required in the case of attacking the system from the external environment. But it requires fewer efforts if a system is attacked internally by the stakeholders of the system. This article presents an access control model that secures the medical data of patients against internal cybersecurity threats. It allows only the legitimate users, that is, authorized patients and doctors to communicate despite the fact of physical boundaries. The proposed model implements authorization in combination with permissions and roles instead of roles only for medical staff. It removes the discrepancies in the existing access control models. The proposed model ensures communication among doctors and patients in a secure, private, and efficient manner. The model is demonstrated by using mathematical modeling along with implementation examples. The proposed model outperformed in comparison with state-of-the-art access control models.

A Dynamic Access Control Model Using Authorising Workflow and Task-Role-Based Access Control

Access control is fundamental and prerequisite to govern and safeguard information assets within an organisation. Organisations generally use web enabled remote access coupled with applications access distributed on the various networks facing various challenges including increase operation burden, monitoring issues due to the dynamic and complex nature of security policies for access control. The increasingly dynamic nature of collaborations means that in one context a user should have access to sensitive information and not applicable for another context. The current access control models are static and lack of Dynamic Segregation of Duties (SoD), Task instance level of Segregation and decision making in real time. This paper addresses the limitations and supports access management in borderless network environment with dynamic SoD capability at real time access control decision making and policy enforcement. This research makes three contributions: i) Defining an Authorising Workflow Task Role Based Access Control using the existing task and workflow concepts. It integrates the dynamic SoD considering the task instance restriction to ensure overall access governance and accountability. It enhances the existing access control models such as RBAC by dynamically granting users access right and providing Access governance. ii) Extended the OASIS standard of XACML policy language to support the dynamic access control requirements and enforce the access control rules for real time decision making to mitigate risk relating to access control such as escalation of privilege in broken access control and insufficient logging and monitoring iii) The model is implemented using open source Balana policy engine to demonstrate its applicability to a real industrial use case from a financial institution. The results show that, AW-TRBAC is scalable consuming relatively large number of complex request and able to meet the requirements of dynamic access control characteristics.

Generic Access Control Model and Semantic Mapping Between Heterogeneous Policies

This article aims to ensure a dynamic set up of access control policies across collaborating organizations where these organizations adopt heterogeneous access control models. To attain this objective, this contribution started with a survey on existing access control models, and their specificities on collaboration. Based on this survey, it remains that the topic on access control collaboration still open despite the efforts made. Therefore, in this article a generic representation of access control concepts is proposed. This generic representation considers the process of semantic mapping between policies of heterogeneous access control systems. In this fact an ontology-based semantic mapping is proposed. This mapping has the advantage to optimize the administrators' involvement by combining linguistic-based and upper-ontology based matching techniques with a user-based constraint strategy for ontology matching.

Visual Attention-Based Access

During collaboration, individual users' capacity to maintain awareness, avoid duplicate work and prevent conflicts depends on the extent to which they are able to monitor the workspace. Existing access control models disregard this contextual information by managing access strictly based on who performs the action. As an alternative approach, we propose managing access by taking the visual attention of collaborators into account. For example, actions that require consensus can be limited to collaborators' joint attention, editing another user's personal document can require her visual supervision and private information can become unavailable when another user is looking. We prototyped visual attention-based access for 3 collaboration scenarios on a large vertical display using head orientation input as a proxy for attention. The prototype was deployed for an exploratory user study, where participants in pairs were tasked to assign visual attention-based access to various actions. The results reveal distinct motivations for their use such as preventing accidents, maintaining individual control and facilitating group awareness. Visual attention-based access has been perceived as more convenient but also less certain when compared to traditional access control. We conclude that visual attention-based access can be a useful addition to groupware to flexibly facilitate awareness and prevent conflicts.

Analysis of Access Control Model for Data Security and Privacy on Multi-Tenant SaaS

Cloud computing has become most trending and emerging technology in recent years and has changed the way of computation and services delivered to customer. Despite all the advantages that cloud provides, users still feel insecure to adopt cloud computing and having major concern over the data security and privacy. This is due to the data of numerous tenants are being located in the same location or database. In this environment data access by unauthorized user is possible. To overcome this issue, there should be a clear boundary for each tenant. Access control model is used to grant the right level of permission to the user in order to carry out their duties, to prevent unauthorized access and to protect assets of organizations and systems. Access control model also can prevent unauthorized user from accessing protected data, ensure authorized users can access protected data and prevent authorized users from performing illegal actions on protected data. There are many types of access control model available in the industry. However, not all the models can be applied in cloud environment due to various reasons. This paper presents an analysis of existing role based access control models. We use evaluation criteria that outlined by NIST for access control system. First, we identified a list of criteria that are suitable to apply in cloud environment specifically on data security and privacy of multi-tenant SaaS application in public cloud. Then, we analysed the existing access control models against the identified evaluation criteria. The analysis outlines the important gaps and missing elements of an access control model that can be extended into an access control model based testing.

Lico: A Lightweight Access Control Model for Inter-Networking Linkages

Processes in operating systems are assigned different privileges to access different resources. A process may invoke other processes whose privileges are different; thus, its privileges are expanded (or escalated) due to such improper “inheritance.” Inter-networking can also occur between processes, either transitively or iteratively. This complicates the monitoring of inappropriate privilege assignment/escalation, which can result in information leakage. Such information leakage occurs due to privilege transitivity and inheritance and can be defined as a general access control problem for inter-networking linkages. This is also a topic that is generally less studied in existing access control models. Specifically, in this paper, we propose a lightweight directed graph-based model, LiCo, which is designed to facilitate the authorization of privileges among inter-networking processes. To the best of our knowledge, this is the first general access control model for inter-invoking processes and general inter-networking linkages.