NewSQL databases like Google Spanner are designed to combine the scalability of NoSQL databases with strong transactional guarantees, making them suitable for microservices transitioning from monolithic systems.

Standardization is the process of transforming data to have a mean of 0 and a standard deviation of 1. This helps in making data more interpretable and suitable for various machine learning algorithms, as it removes the scale effect.

To combat the vanishing gradient problem in RNNs, a common approach is to use Long Short-Term Memory (LSTM) units. LSTMs are designed to alleviate the vanishing gradient issue by allowing gradients to flow over longer sequences.

The "right to explanation" is important as it promotes transparency in AI decision-making. In ethical AI, users should have insight into how AI algorithms arrive at their decisions. This transparency is vital to prevent bias, discrimination, and unethical decision-making, making it a critical aspect of AI ethics.

Perfective maintenance involves making changes to enhance system performance, improve maintainability, and optimize the software. It includes activities like code refactoring and efficiency improvements.

The Maintenance model of software evolution is centered around the continual alteration of the software system to adapt it to varying environments and changing requirements. This phase is critical for keeping the software functional and relevant over time.

Dynamic Agents Provisioning is a sophisticated strategy for scaling Jenkins efficiently in a large-scale environment. It allows Jenkins to dynamically provision and de-provision agents based on workload, ensuring optimal resource utilization.

The statelessness of RESTful APIs simplifies server-side scalability since each request from a client contains all necessary information, and servers don't need to maintain session state. However, it may require client-side state management for complex interactions. This is important to understand in the context of designing efficient, scalable systems.

In this scenario, OAuth 2.0 is used for user authentication to obtain an access token securely. JWT is then used for authorization by including user claims in the token, specifying what the user is allowed to access within the SPA. This separation of concerns allows for a secure and flexible way to manage user authentication and authorization.

Optimizing the performance of an API involves maximizing its speed and efficiency. This includes reducing response times, minimizing resource usage, and ensuring the API can handle a high volume of requests while delivering results quickly and reliably. Performance is a key consideration for successful APIs.

When selecting an API Gateway for a microservices architecture, you must consider various factors, including security and authentication options to protect your APIs, performance and scalability features for handling traffic, API versioning to manage changes, and documentation support to make APIs easily discoverable. Additionally, logging and monitoring capabilities are crucial for troubleshooting and maintaining the health of your services.

When building APIs with ASP.NET Core, developers can use Swagger/OpenAPI to define the routes, controllers, and actions. Swagger is a popular tool for documenting and defining APIs in a machine-readable format, making it easier to create and consume web APIs in ASP.NET Core.