I belive that both inputs and specifications have their intended purposes. In terms of actually constructing a device, it is impossible to do so based on solely inputs. Specifications are needed for the actual construction of the device and for the device to be constructed identically during the manufacturing process. However, inputs are important because they lay out how the design meets the intended needs without going into unnecessary detail. For instance, when describing a project to a group of investors, it is much more useful to talk to them about the inputs rather than the specifications. The inputs as the question of how the device works without the unnecessary details such as individual measurements or tolerances. Also, you need an input document in order to make a specifications document. 

The Design Input Document (DID) and Design Specification Document (DSD) are both important for developing a medical device, but they serve different purposes. The DID provides a broad overview of the product concept, describing what the device should do and what the customer or user needs. It’s more qualitative and helps the team visualize the product’s goals and appearance. The DSD, on the other hand, gives quantitative technical details—such as measurements, materials, and tolerances—that guide manufacturing and ensure product consistency. The main advantage of the DID is flexibility and creativity during early development, while the DSD ensures precision and compliance with regulatory and quality standards. Without the DID, designers might lose sight of user needs; without the DSD, the product might not meet safety or performance requirements. 

In terms of design controls, the connection between the Design Input Document (DID) and the Design Specification Document (DSD) is essential to guaranteeing that a product is created methodically, precisely, and in accordance with legal requirements. In the process of developing a product, each has a specific function: the DSD specifies how the device will fulfill its requirements, while the DID specifies what the device must perform. Effective communication and responsibility throughout the project depend on this separation, which guarantees clarity between engineering execution and user needs. The DSD outlines how to turn that vision into a concrete, testable, and manufacturable reality, while the DID explains why the product should exist and what it should accomplish from a functional and therapeutic standpoint. Together, they provide the basis for traceability, which is essential to FDA and ISO 13485 design control compliance and guarantees that each design choice can be linked to an original user requirement. Without one, the process is either too restricted or too unclear. This raises the question of which document, in your perspective or experience, is more difficult to accurately maintain: the DSD with its intricate engineering limitations or the DID with its changing user requirements. In the end, the DID and DSD are complementary components of a single, well-managed design process. One guarantees that the device performs its intended function in a safe and efficient manner, while the other guarantees that the design can be consistently produced in accordance with those criteria. When combined, they safeguard the patient's safety as well as the product's integrity, which is the ultimate objective of any medical device development endeavor.

Understanding customer needs and translating them into clear design inputs is a fundamental step in medical device development, typically documented in the Design Input Document (DID). Customer needs, gathered from clinicians, patients, and other end users, are analyzed and converted into measurable, testable requirements within the DID. These inputs then guide the creation of the Design Specification Document (DSD), which details the engineering and technical parameters necessary to meet those needs. A well-prepared DID ensures that the DSD accurately reflects safety, performance, and usability expectations. Failure to properly document and link customer needs in the DID and DSD can lead to design gaps, usability problems, or noncompliance with regulatory standards. Continuous communication among design, clinical, and regulatory teams ensures that these documents stay aligned throughout development. Ultimately, well-structured DID and DSD documents help ensure that the final medical device meets user expectations, regulatory requirements, and clinical performance goals.