Submitted:
07 January 2026
Posted:
07 January 2026
Read the latest preprint version here
Abstract
Modern information systems suffer from a fundamental architectural flaw: data coherence depends on external validation layers, creating systemic entropy and computational waste. We present the G Model, a mathematical framework that redefines informationas points in a geometric space where incoherence is mathematically impossible. Through a triaxial formalization (Meaning, Location, Connection) and an intrinsic coherence operator (Φ), the system guarantees that only valid data can exist within the managed universe (Ω). We formalize this with four fundamental axioms ensuring coherence, uniqueness, acyclicity, and deterministic propagation. Our implementation, the SRGD system (Sistema Relacional Gestión de Datos), demonstrates practical viability through a stateless three-layer architecture and unified flow patterns. Preliminary results show significant advantages in critical infrastructure scenarios where error is inadmissible, providing a foundation for trustworthy AI training data and eliminating the validation overhead present in traditional RDBMS and NoSQL systems. This work represents a paradigm shift from “data storage systems” to “coherent information spaces".
Keywords:
database theory
; data coherence
; geometric data models
; formal verification
; information systems architecture
1. Introduction
1.1. Motivation
For the past five decades, data management has been anchored in the “passive container” paradigm. Both Relational Database Management Systems (RDBMS) following Codd’s model [1] and their modern derivatives (NoSQL, NewSQL) operate under a dangerous separation: storage is the database’s responsibility, while logical coherence is delegated to external application layers.
This fragmented approach generates what we term Systemic Entropy:
- External Validation: Data integrity depends on fallible, mutable middleware external to the data itself
- Coherence Latency: A temporal gap exists between data mutation and consequence propagation
- Structural Fragility: Relationships (Foreign Keys) are mere pointers, not strict causal links
- Computational Waste: Continuous validation and redundant data processing
Current approaches attempt to resolve this through increased computing power and software patches (triggers, complex stored procedures). However, this is building on foundations of sand: the underlying architecture continues treating information as “static cells” rather than dynamic vectors with geometric properties.
1.2. Research Questions
This work addresses three fundamental questions:
RQ1: Can data coherence be guaranteed mathematically rather than validated procedurally?
RQ2: What formal framework enables intrinsic coherence while maintaining computational efficiency?
RQ3: How can such a theoretical model be implemented in practical, scalable systems?
1.3. Contributions
Our main contributions are:
- 1.
- The G Model: A formal geometric framework for information spaces where incoherence is mathematically impossible (Section 3)
- 2.
- Four Fundamental Axioms: Formal guarantees of existence, uniqueness, acyclicity, and propagation determinism (Section 3.3)
- 3.
- SRGD Normal Forms: Five semantic normal forms extending Codd’s work to the temporal and semantic domains (Section 3.5)
- 4.
- SRGD Architecture: A practical three-layer, stateless architecture implementing the G Model (Section 4)
- 5.
- Unified Flow Pattern: A single architectural pattern for all data channels (UI, IoT, APIs, AI) ensuring universal coherence (Section 4.3)
- 6.
- RM/O Algebra: A formal model for UI objects guaranteeing local coherence before global validation (Section 5)
1.4. Paper Organization
Section 2 reviews related work. Section 3 formalizes the G Model. Section 4 describes the SRGD system architecture. Section 5 presents the RM/O algebra for user interfaces. Section 6 discusses implementation and preliminary results. Section 7 analyzes implications and limitations. Section 8 concludes.
2. Related Work
2.1. Traditional Database Systems
Codd’s Relational Model (1970) [1] established the foundation of modern RDBMS through set theory and first-order predicate logic. The model defines relations as subsets of Cartesian products and introduces normalization (1NF-5NF) to eliminate redundancies. However, Codd’s model treats coherence as external constraints (PRIMARY KEY, FOREIGN KEY, CHECK) that must be enforced by the DBMS engine or application logic.
Limitations:
- Coherence is reactive (validated after attempted violation)
- Complex business rules require external triggers/procedures
- No formal propagation model for calculated values
Date’s Relational Model [2] refines Codd’s work but maintains the same fundamental separation between data and coherence logic.
2.2. NoSQL and NewSQL Systems
NoSQL databases (MongoDB, Cassandra, DynamoDB) sacrifice ACID guarantees for scalability, often implementing eventual consistency [3]. This exacerbates coherence problems, as the system explicitly allows temporary incoherent states.
NewSQL systems (CockroachDB, Google Spanner) attempt to combine SQL semantics with NoSQL scalability [4], but still rely on external validation layers and don’t address the fundamental coherence problem.
2.3. Graph Databases
Graph-oriented databases (Neo4j, ArangoDB) [5] explicitly model relationships as first-class entities, similar to our F axis. However:
- Coherence still requires external validation
- No native distinction between base and calculated values
- No formal acyclicity guarantees in the data model
2.4. Constraint Programming and Formal Methods
Alloy [6] and Z notation [7] provide formal specification languages for system invariants. However, these are specification tools, not execution models. They verify designs but don’t implement self-coherent data structures.
Active Databases [8] introduced ECA (Event-Condition-Action) rules to embed logic in the database. While promising, triggers remain imperative constructs, not declarative mathematical guarantees.
2.5. Type Systems and Dependent Types
Dependent type systems [9] (Coq, Agda, Idris) allow types to depend on values, enabling compile-time correctness proofs. Our operator shares philosophical similarities, but operates at the data level rather than the program level, and provides runtime guarantees in production systems.
2.6. Gaps in Literature
No existing system provides:
- 1.
- Intrinsic coherence where invalid data cannot exist (not just “shouldn’t”)
- 2.
- Geometric formalization of information with topological properties
- 3.
- Deterministic propagation distinguishing base from calculated data
- 4.
- Unified architecture treating all data sources (UI, IoT, APIs) identically
- 5.
- Formal algebra extending coherence guarantees to the UI layer
The G Model addresses these gaps.
3. The G Model: Formal Framework
3.1. Global Information Space (G)
We define the Global Information Space as a set of points g determined by a triaxial vector:
where:
- (Meaning Axis): Attribute defining data nature, subject to norms
- (Location Axis): Unique identity key in the universe,
- (Connection Axis): Foreign keys establishing graph topology,
Definition 1
(Information Point).
3.2. The Coherent Management Universe ()
Unlike traditional systems that permit inconsistent states, the real management universe is defined exclusively as the subset of G where the Coherence Operator equals unity:
Definition 2
(Coherent Universe).
Definition 3
(Coherence Operator).
For each attribute a, the operator evaluates compliance with all applicable norms:
Property 1
(Impossibility of Incoherence).
This is not a validation that rejects; it’s a geometric property that prevents existence.
3.3. Fundamental Axioms
The G Model is governed by four irreducible axioms:
Axiom 1
(Existence by Coherence).
Implication: The “erroneous datum” does not exist within the system. Error is an external anomaly that fails to crystallize in .
Axiom 2
(Uniqueness of Location).
Implication: The location axis is orthogonal and unique; there is no positional ambiguity.
Axiom 3
(Direction and Non-Circularity). Three properties ensure acyclicity:
- 1.
- Irreflexivity:
- 2.
- Asymmetry:
- 3.
- Acyclic Transitivity:
Implication: The dependency graph is necessarily a DAG (Directed Acyclic Graph), guaranteeing algorithm termination and system stability.
Axiom 4
(Determinism of Propagation).
- If , the point is Base (source of information)
- If , the point is Calculated (dependent on vector )
Implication: The system knows exactly which pieces to “move” when something changes, optimizing processing to the minimum necessary level.
3.4. Propagation Dynamics
Definition 4
(Dependency Graph).
Definition 5
(Propagation Vector).
Theorem 1
(Optimal Propagation). When a base datum changes, only points in require recalculation, achieving complexity rather than .
Proof.
By Definition 5, contains exactly the calculated points reachable from through the dependency relation. By Axiom 3, the dependency graph is acyclic, so ≺ defines a partial order. A point means either (doesn’t depend on anything) or g is not reachable from through ≺. In both cases, changing cannot affect . Since and typically , complexity is . □
3.5. SRGD Normal Forms
While Codd’s normal forms (1NF-5NF) eliminate syntactic redundancies, SRGD Normal Forms extend into semantic and temporal domains:
Definition 6
(SRGD-FN1: Intra-table Semantic Grouping).
Each table represents a complete entity with unitary semantic meaning, without NULL values.
Definition 7
(SRGD-FN2: Systemic Unification of Equivalent Entities).
Semantically identical entities unify into a single systemic structure.
Definition 8
(SRGD-FN3: Semantic Hierarchization).
Entities organize into hierarchies where upper categories capture common properties.
Definition 9
(SRGD-FN4: Relational Emergence of Roles).
Roles are not static attributes but emerge dynamically from active relationships.
Definition 10
(SRGD-FN5: Temporal Semantic Coherence).
Value propagation is governed by algebraic conditions activated or fixed according to relationship states, guaranteeing coherence over time without imperative intervention.
4. SRGD System Architecture
4.1. Three-Layer Transversal Architecture
The SRGD system materializes the G Model through a three-layer architecture that operates transversally across all data flows (UI, Peripherals, External APIs, AI).
4.1.1. Persistence Layer (Services Layer)
Contains four fundamental repositories:
- Structure Repository (): Stores all system metadata, norms, form definitions, validation rules, and flow configurations
- Coherent Database (): Physical materialization of space G. Inviolable rule: only stores points g where
- Peripherals Registry: Catalog of connected devices (IoT sensors, printers) with communication protocols
- External Services Gateway: Manages external API configurations, field mappings, and webhook management
Key principle: Calculations are delegated. Business logic constructs SQL queries that resolve aggregations directly in the optimized database engine.
4.1.2. Development Layer (Business Layer)
Implements specific logic for each system flow:
Key Responsibilities:
- Receives and parses incoming requests
- Constructs optimized SQL with JOIN according to graph and aggregations (SUM, COUNT, AVG)
- Applies Coherence Operator before any write operation
- Rejects data where , ensuring only points belonging to reach persistence
- Formats outputs according to destination channel
4.1.3. Presentation Layer (User Interface)
Responsible for rendering visual structures, user interaction, and local validation:
- Mounts structures from scripts generated by business layer
- Instantiates visual objects according to RM/O model
- Marks each object with propagation determinant
- Implements Local Validation (): each object validates its own state
- Containers aggregate child validations:
- Maintains a Temporal Buffer for pending modifications (UI-only)
4.2. Stateless Request-Response Communication
The system does NOT maintain connections, sessions, or object instances open on the server between requests.
4.2.1. Complete Request Lifecycle
Each interaction follows 11 steps:
- 1.
- UI launches request to Web Service
- 2.
- Web Service receives request (listener), opens channel
- 3.
- Opens database connection (from pool)
- 4.
- Reads in (structure repository)
- 5.
- Constructs SQL with aggregations
- 6.
- Executes SQL and receives response (already calculated)
- 7.
- Closes database connection (returns to pool)
- 8.
- Constructs response, applies if write operation
- 9.
- Sends response to UI
- 10.
- Closes communication channel
- 11.
- UI processes response
After step 10: NOTHING remains in server memory.
4.3. Unified Flow Architecture
Master Pattern: All information, regardless of origin channel, follows:
Five Orthogonal Flows:
- : User interface (HTML+JS)
- : Peripherals (IoT, printers, sensors)
- : External systems outbound (API calls)
- : External systems inbound (webhooks)
- : AI interaction (natural language queries)
Axiom 5
(Flow Orthogonality).
Activity in one flow does not affect latency or capacity of another.
5. RM/O Model: UI Algebraic Behavior
The presentation layer is not mere visualization but a formal system with its own algebra.
5.1. Visual Object Definition
Definition 11
(Visual Object).
where:
- : Projected attributes from data graph
- M: Encapsulated validation methods ()
- E: Visual-operational state properties (visible, enabled, editing)
- : Declarative signals (events)
5.2. Hierarchical Coherence
Local Coherence Operator ():
Containers (): Special objects grouping other objects.
Global Coherence Operator ():
A form is coherent if and only if all its fields are coherent.
5.3. Atomicity in Transfer to
Definition 12
(Transfer Morphism).
Atomicity Principle: Transfer only executes if .
All-or-nothing: If a single field is incoherent, complete transfer is blocked.
5.4. Formal Properties
- Invariant 1.
- (Binary coherence)
- Invariant 2.
- (Coherence aggregation)
- Invariant 3.
- (Autonomy)
- Invariant 4.
- (Transfer atomicity)
Theorem 2
(Transitive Coherence).
Theorem 3
(Impossibility of Inconsistency).
6. Implementation and Results
6.1. Prototype Implementation
We implemented a functional SRGD prototype:
Technology Stack:
- Backend: C# / .NET Core (business layer)
- Database: SQL Server ( implementation)
- Frontend: HTML5 + JavaScript (RM/O model)
- Communication: RESTful API (stateless)
Metrics:
- Lines of code: ∼45,000 (backend), ∼12,000 (frontend)
- Repository: 23 meta-tables defining structures
- Test Database (): 150 base tables, ∼50 calculated views
- Complexity of H: Max depth 8 levels, avg 3.2
- Size of vectors: Avg 4.7 dependent points per base change
6.2. Experimental Validation
6.2.1. Experiment 1: Coherence Guarantee
Hypothesis: It is impossible to insert incoherent data.
Method: Attempted 10,000 INSERT operations with deliberately invalid data (NULL required fields, out-of-range values, violated referential integrity).
Results:
- Operations rejected by : 10,000 (100%)
- Incoherent data in : 0 (0%)
- Validation: Axiom 1 confirmed empirically
6.2.2. Experiment 2: Propagation Efficiency
Hypothesis: Propagation is surgical (only affects , not all ).
Method: Modified 1,000 random base records (). Measured which points required recalculation.
Results:
Table 1.
Propagation Efficiency Results.
| Change Type | Avg | Total | Efficiency |
|---|---|---|---|
| Simple field | 2.3 | 125,000 | 99.998% savings |
| Related entity | 15.7 | 125,000 | 99.987% savings |
| Deep hierarchy | 47.2 | 125,000 | 99.962% savings |
Conclusion: Propagation is , confirming Theorem 1.
6.2.3. Experiment 3: Stateless Scalability
Hypothesis: Stateless model enables trivial horizontal scaling.
Method: Load test with 1, 2, 4, 8 server instances. Measured throughput and latency.
Results:
Table 2.
Horizontal Scaling Results.
| Servers | Throughput (req/s) | Scaling Factor | P95 Latency (ms) |
|---|---|---|---|
| 1 | 450 | 1.0x | 87 |
| 2 | 895 | 1.99x | 89 |
| 4 | 1,780 | 3.96x | 91 |
| 8 | 3,520 | 7.82x | 94 |
Conclusion: Near-linear scaling with minimal latency degradation, validating stateless architecture.
6.3. Case Study: Critical Financial System
Context: Implementation in a high-frequency trading support system where error is inadmissible.
Requirements:
- Positions, orders, risk exposures must be always coherent
- Propagation latency ms
- Zero tolerance for inconsistent states
Implementation:
- Positions and orders as ()
- Risk exposure as (, depends on )
- 47 coherence norms in (position limits, margin requirements)
Results After 6 Months:
- Incoherent states detected: 0
- rejections (attempted rule violations): 127
- Avg propagation time: 23ms (P95: 41ms)
- System availability: 99.97%
Comparison vs. Previous System (traditional RDBMS with application-level validation):
- Incoherent states (6 months): 14 incidents
- Avg recovery time per incident: 47 minutes
- Financial impact of incidents: €2.3M
SRGD Impact: Zero incidents, zero financial losses from data incoherence.
7. Discussion
7.1. Theoretical Implications
Paradigm Shift: The G Model represents a transition from “data storage systems” to “coherent information spaces.” Coherence is not a goal to achieve but an inherent, inescapable property.
Relationship to Type Theory: The operator shares philosophical similarities with dependent types [9], but operates at runtime on data values rather than compile-time on program terms.
Topological Properties: By treating information as geometric space, we inherit mathematical properties: H as DAG, as filtered subspace, as reachability set.
7.2. Practical Advantages
- 1.
-
Infrastructure:
- Stateless model → Trivial horizontal scaling
- No sessions → Kubernetes-native, instant recovery
- Connection pool → Resource efficiency without complexity
- 2.
-
Critical Systems:
- Mathematically guaranteed coherence → Suitable for finance, energy, defense
- Zero incoherent states → Case study validates this
- Surgical propagation → Real-time performance maintained
- 3.
-
AI Training Data:
- Clean-by-design → Eliminates hallucination from incoherent training data
- Traceable H → Full lineage for any conclusion
- Explainable → Documents how calculated values are derived
7.3. Limitations and Future Work
Theoretical Limitations:
- 1.
- Computational Complexity: While is much smaller than , computing for deep hierarchies can approach . Future work should explore incremental H computation.
- 2.
- Distributed : Current formalization assumes single-authority . Extending to distributed consensus (Raft, Paxos) while maintaining Axiom 1 is an open problem.
- 3.
- Temporal Queries: SRGD-FN5 addresses temporal coherence but doesn’t provide a full temporal query algebra. Integration with temporal databases [10] needs formalization.
Practical Limitations:
- 1.
- Migration Complexity: Migrating existing systems to SRGD requires rethinking data models according to SRGD-FN1-5. Automated migration tools are needed.
- 2.
- Developer Mindset: Traditional developers are accustomed to imperative validation. SRGD’s declarative coherence requires training and cultural shift.
- 3.
- Performance Edge Cases: Extremely large vectors ( points) can create bottlenecks. Parallel propagation strategies need investigation.
Future Research Directions:
- 1.
- Formal Verification: Use Coq or Isabelle to machine-verify Axioms 1–4 and Theorem 1.
- 2.
- Distributed G Model: Formalize extension to multi-node with eventual or strong consistency guarantees.
- 3.
- Machine Learning Integration: Explore using as training corpus for LLMs, measuring reduction in hallucinations.
- 4.
- Benchmark Suite: Develop standard benchmarks comparing SRGD against traditional RDBMS, NoSQL, and graph databases.
7.4. Comparison with Related Work
Only SRGD provides intrinsic coherence, deterministic propagation, stateless architecture, and extends guarantees to the UI layer.
8. Conclusions
We presented the G Model, a mathematical framework redefining information as points in a geometric space where incoherence is impossible by construction. Through four fundamental axioms, we formalize coherence, uniqueness, acyclicity, and deterministic propagation. Our implementation, the SRGD system, demonstrates practical viability via a stateless three-layer architecture and unified flow patterns.
Key Findings:
- 1.
- Coherence is achievable as an intrinsic mathematical property (answering RQ1)
- 2.
- Geometric formalization with operator and propagation vector enables efficient implementation (answering RQ2)
- 3.
- Stateless architecture with -driven flows allows practical, scalable deployment (answering RQ3)
Validation: Experiments confirm zero incoherent states, surgical propagation (99.96%-99.99% efficiency), and near-linear horizontal scaling. A financial case study demonstrates zero incidents over 6 months vs. 14 incidents in traditional system.
Impact: This work challenges the 50-year paradigm of external coherence validation, offering a foundation for:
- Trustworthy AI (clean training data)
- Critical infrastructure (mathematically guaranteed coherence)
- Cloud-native systems (stateless, Kubernetes-ready)
Future Directions: Distributed formalization, formal verification in Coq, machine learning integration, and comprehensive benchmark development.
The G Model transforms data management from “storage systems” to “coherent information spaces,” making the impossible errors of yesterday mathematically impossible today.
Appendix A. Formal Proofs
Appendix A.1. Proof of Theorem 1 (Optimal Propagation)
Theorem A1
(Restatement of Theorem 1). When base datum where changes, only points in propagation vector require recalculation.
Proof. 1. By Definition 5,
- 2.
- This means contains exactly the calculated points reachable from through the dependency relation.
- 3.
- By Axiom 3, the dependency graph is acyclic. Therefore, ≺ defines a partial order.
- 4.
-
A point means either:
- (), so it doesn’t depend on anything, or
- g is not reachable from through ≺, meaning no path of dependencies connects to g
- 5.
- In both cases, changing cannot affect since there’s no dependency path.
- 6.
- Therefore, only needs recalculation.
- 7.
- Since and typically , complexity is .
□
Appendix A.2. Proof of T2 (Impossibility of Inconsistency)
Theorem A2
(Impossibility of Inconsistency). If form coherence is false, no values can transfer to Ω. Formally:
Proof. 1. By the definition of transfer morphism (Section 5), executes only if .
- 2.
- Suppose .
- 3.
- Then by the definition of :
- 4.
- This means (no transfer occurs for any child object).
- 5.
- By Axiom 1, only points g where can exist in .
- 6.
- Since means no value reaches the validation step, no point is even proposed to .
- 7.
- Therefore, incoherent values cannot enter , not even to be rejected.
□
Appendix B. SRGD vs Traditional RDBMS Feature Matrix
Table A1 presents a comprehensive comparison between traditional RDBMS architectures and the SRGD system implementing the G Model.
Table A1.
Comprehensive Comparison: SRGD vs Traditional RDBMS.
| Feature | Traditional RDBMS | SRGD (G Model) |
|---|---|---|
| Coherence Location | External (application layer) | Intrinsic ( operator) |
| Incoherent State Possible | Yes (temporarily) | Mathematically impossible |
| Propagation Model | Triggers (imperative) | vector (declarative) |
| Dependency Graph | Implicit | Explicit DAG (H) |
| Base vs Calculated | Not distinguished | Formal ( determinant) |
| Stateless Architecture | No (requires sessions) | Yes (by design) |
| Horizontal Scaling | Complex (session management) | Trivial (no shared state) |
| UI Coherence Model | Ad-hoc validation | Formal algebra (RM/O) |
| Multi-channel Guarantee | Per-channel logic | Unified ( for all flows) |
| Recovery Time (failure) | Minutes (session restoration) | Milliseconds (stateless) |
| Formal Axioms | None | Four (Axioms 1–4) |
| Semantic Normal Forms | 5 (syntax only: 1NF-5NF) | 10 (5 classical + 5 semantic/temporal) |
The key differentiator is that traditional systems attempt to maintain coherence after data entry through validation, while SRGD prevents incoherent data from existing in the first place through mathematical impossibility.
References
- Codd, E. F. A Relational Model of Data for Large Shared Data Banks. Communications of the ACM 1970, 13, 377–387. [Google Scholar] [CrossRef]
- Date, C. J. An Introduction to Database Systems, 8th ed.; Addison-Wesley: Boston, 2003. [Google Scholar]
- DeCandia, G.; et al. Dynamo: Amazon’s Highly Available Key-value Store. ACM SIGOPS Operating Systems Review 2007, 41, 205–220. [Google Scholar] [CrossRef]
- Pavlo, A.; Aslett, M. What’s Really New with NewSQL? ACM SIGMOD Record 2016, 45, 45–55. [Google Scholar] [CrossRef]
- Angles, R.; Gutierrez, C. Survey of Graph Database Models. ACM Computing Surveys 2008, 40, 1–39. [Google Scholar] [CrossRef]
- Jackson, D. Software Abstractions: Logic, Language, and Analysis; MIT Press: Cambridge, 2012. [Google Scholar]
- Spivey, J. M. The Z Notation: A Reference Manual, 2nd ed.; Upper Saddle River: Prentice Hall, 1992. [Google Scholar]
- Paton, N. W.; Díaz, O. Active Database Systems. ACM Computing Surveys 1999, 31, 63–103. [Google Scholar] [CrossRef]
- Pierce, B. C. Types and Programming Languages; MIT Press: Cambridge, 2002. [Google Scholar]
- Jensen, C. S.; et al. The Consensus Glossary of Temporal Database Concepts. ACM SIGMOD Record 1994, 23, 52–64. [Google Scholar] [CrossRef]
- Lamport, L. Time, Clocks, and the Ordering of Events in a Distributed System. Communications of the ACM 1978, 21, 558–565. [Google Scholar] [CrossRef]
- Hellerstein, J. M.; Stonebraker, M.; Hamilton, J. Architecture of a Database System. Foundations and Trends in Databases 2007, 1, 141–259. [Google Scholar] [CrossRef]
- Abiteboul, S.; Hull, R.; Vianu, V. Foundations of Databases; Addison-Wesley: Boston, 1995. [Google Scholar]
- Kleppmann, M. Designing Data-Intensive Applications; O’Reilly Media: Sebastopol, 2017. [Google Scholar]
- Robinson, I.; Webber, J.; Eifrem, E. Graph Databases: New Opportunities for Connected Data, 2nd ed.; O’Reilly Media: Sebastopol, 2015. [Google Scholar]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Copyright: This open access article is published under a Creative Commons CC BY 4.0 license, which permit the free download, distribution, and reuse, provided that the author and preprint are cited in any reuse.