“…shall support…” Requirements
This type of requirement is used to flow an upper-tier (parent) requirement topic to a lower-tier (child) specification when the System Engineer either does not understand how the requirement can (or should) be portioned between the subordinate (child) CI’s, or is afraid to commit under contract. Requirements written in this form are essentially useless: either... read more
A-Spec
A type of specification covering an entire complex system, or a major portion of one. As far as I can tell, the term appears to have originated with MIL-STD-490. A good statement of purpose is in DI-CMAN-80008: the A-spec was used to define and partition the requirements allocable to all or part of a system…... read more
Abductive Reasoning
Painting with a broad brush, abductive reasoning1 occurs when we seize upon the simplest plausible explanation for (at least) the important observations. In effect, it works backwards from observation of consequences to explain them by way of the minimum possible number of degrees of freedom2. See also reasoning. Contrast with inductive reasoning and deductive reasoning. We... read more
Acceptance
A contractual event held for each deliverable copy1 of a CI to establish concurrence between supplier and customer that the subject CI meets (or acceptably deviates from) the previously established Acceptance Requirements for its correct manufacture. An acceptance event is associated with each Serial Number or Lot Number, depending on how the item is procured... read more
Acceptance Requirement
A design-specific type of technical requirement used to verify that an as-built built item is, in fact, a specimen of that design to within the tolerances established as part of that design. Often referred to as an “Acceptance Criterion”. Contrast with Qualification Requirement, which establishes
Accession Identifier
A library science term meaning the identifier used to define exactly one version of a document in a repository or configuration controlled list; a “find” number (e.g., Library of Congress number, ISBN). The ability to reliably get hold of exactly the thing desired is, of course, critical. See also Relational Database.
Accuracy
The correctness of a value with respect to absolute truth. See also tolerance and precision.
Acquisition Customer
The Department of Defense separates the procurement of materiel (“Acquisition”) from the use of materiel (e.g., Combat, Logistics). The End User owns the Operational Requirements, but has no contractual relationship with the Developer. The Acquisition Customer is charged with “translating” the Operational Requirements into contractually obligated Technical Requirements for use by the Developer. The basic... read more
Addendum Specification
Exactly as it sounds: a piece of a specification which, for whatever reason, has not been published as a physical part of the main document body. An addendum does not stand on its own, but is part of the specification, and its provisions carry the same force. Examples of addenda include classified material (which can... read more
Administrative Control Number
A number that looks like and is treated like a real Part Number, but isn’t one. Administrative control numbers can be used to “cover” groups of interchangeable items (see, for example, VICD) or can “cover” groups of items contributing to Make-on-Assembly CI’s. See also the CI Development Cycle (Intermediate).
Administrative Independence
A condition in which two organizations intentionally do not share some particular set of goals. Administrative Independence is usually established to at least partially substantiate that one of the two organizations can plausibly provide cognitively unbiased witnessing of execution by the other. The witnessing group is often rigidly process-oriented, with many intermediate opportunities to document... read more
Algorithm
An abstract set of steps (tasks or logical instructions which may, or may not, include parallelization) having a defined, internally managed set of termination criteria. Contrast with process.
Allocable Requirement
A requirement where the measure(s) can (and should) be apportioned between the allocation target’s constituent parts. A non-allocable requirement must be passed to the subordinate parts in its entirety. This term disappeared somewhere in the late 1980’s, probably because it was too easily confused with the concept of “requirement allocation”. That was too bad, because... read more
Allocation
The act of formally designating a relationship between two (or more) things or concepts. For example, we allocate technical requirements to CI‘s when a development specification is authenticated (but not before!).
Allocation Target
The subordinate widget (which may be either concrete or abstract in nature) to which an allocation is made (e.g., a requirement being assigned to a CI).
Altered Item Drawing
As defined by ASME Y14.24, an Altered Item Drawing does exactly what its name says: it modifies some other part by adding and/or subtracting features. The original part is usually under the configuration control of some other design activity (usually a different company) or is the subject of some national standard. This drawing type is... read more
Analog Computer
A computational device that models (often differential) equations as an electrical circuit and, therefore, requiring all problems to be recast in the form of circuit design. For the most part, analog computers have been replaced by digital computers, but idea was exceedingly cool, and wonderful things could be accomplished with it.
Analysis
Analysis is the process of examining a thing by identifying its constituent parts and describing the relationships between them. Contrast with synthesis. As a verification method, analysis is the inference (by extrapolation, interpolation, logic, etc. using some algorithm) of the value(s) for some characteristic using validated models and engineering relationships. The method is applicable IFF... read more
Analytic Function
Simplistically, a mathematical expression that is (at least locally) representable as a convergent power series on an open interval (in the Real Domain – the issue is more complex in the…Complex…Domain). Being expressed as a convergent power series means that the function is infinitely differentiable, therefore its value in the region around any given point... read more
Ancillary Drawing
In the ASME Y14.24 context, any drawing that is not identifying. Ancillary drawings are most often used to document Engineering information that is better understood in graphical form (as opposed to textual), but is not mandatory for the manufacture of the subject part. This concept can confuse Engineers who do not have a strong design... read more
Anecdotal Data
Data that are offered without objective substantiating evidence. In the case of the present document, often “what I recall being told as a young ‘un”. Lack of objective evidence doesn’t mean the data are wrong. It just means they cannot be accepted as definitive.
Application (as in “Application Block”)
A combination of CI and position(s) in the purchasing sequence thereof. In the limit case, the position might be just a single delivery to a customer. The combination can be used to explicitly limit the range in a production stream at which a particular version of a production drawing is to be used. In certain... read more
Application Software
The software that an End User directly interacts with to accomplish some operationally relevant task (“business logic”). Application software is usually specific to an OS, or OS family, but can be written so as to be portable. Application software is sometimes referred to as a “program”, “application program” or, more recently, an “app”. See also... read more
Archetype
An archetype is the original model, form, or pattern from which something is made or developed1. It is useful and instructive to further quote the example from the source: “in…oral ballads, variation has gone so far that it is impossible to reconstruct the exact words of the [archetype] .” (my emphasis). An archetypical example can... read more
Array
An array is a sequential list1 of values, where position in the sequence denotes some particular relevance to the user. Arrays may take any order. We allow degenerate forms to exist, so that scalars and vectors can also be considered arrays. When the positions in the listing require exactly two numbers2 for access, an array is often referred... read more
Article
An instance of a design. See also Serial Number. Often used in the context of a “test article” (see also UUT).
ASME Y14.24
“Types and Applications of Engineering Drawings” (an American National Standard). This is the definitive industry source for what “drawings” are, what types there are, and how they are to be used. It should be studied thoroughly, because this is how the rest of the known universe expects us to communicate (except when we spend several months... read more
Assembly Operations: Grapple, Berth, and Dock
NSTS 214921 identifies three legacy on-orbit operations of immediate interest: grappling, berthing, and docking. These three operations, from which most present-day concepts descend, can be abstracted as different mechanical means of one spacecraft asserting Control Authority2 over the trajectory and attitude of a cooperating spacecraft3: “Payload Bay User’s Guide”, Johnson Space Center (2000)[↩] Used here... read more
Associate Contractor Agreement (ACA)
A contractual document coordinating the work between two developing organizations both of which are sub-contracting from the same superior organization but otherwise having no direct contractual relationship with respect to the Prime Contract in question. An ACA is developed by concurrence between the two at the direction of their immediate contractual superior which may, or... read more
Audit
A formal examination determining the degree to which pre-specified criteria have been met by a purportedly responsive article, design, process or combination thereof. An audit occurs “after the fact”, when the developmental project is claimed to have been completed. Contrast with Review, with which there can be some bureaucratic overlap.
Authentication
A contractual process used to formalize concurrence at PDR by the Acquisition Customer with development requirements allocated to a CI. In effect, it forced the Developer to admit to intended capability for each CI and also (importantly) forced the Acquisition Customer to commit to paying for development if compliance were shown at FCA. More recently,... read more
Authorized Representative (AR)
An industry engineer (such as a Boeing employee) authorized by the FAA to approve Certification data on behalf of the FAA for an aircraft’s Type Certification. The authorization applies to non-retained regulatory requirements only. An AR is paid by the Commercial Developer, but has an enforceable legal responsibility to the FAA. The term is applicable... read more
B-spec
Short for “Type B Specification” in the MIL-STD-490 framework. A development specification.
Bake Your Noodle
Some of our brains heat up pretty bad when we think too hard.
Baseline
A formally acknowledged set of information establishing a frame of reference from which deviation or departure can be measured (see also basis). The concept of a “baseline” should be thought of as a practical reaction to the observer effect1 in Physics: watching too closely impacts the work being done. With a baseline, management can permit... read more
Basis
A set of orthogonal (mutually independent) vectors (or functions) that can be used to unambiguously identify exactly one region in an abstract space of interest. When used in the context of technical requirements: the list of topics (some or all of which might be functions) which, when we are talking about any one of them,... read more
Basis of Estimate (BoE)
The underlying logic used to estimate the resources needed to execute a contract change action (including, but not limited to, a proposal1). The BoE can be parameterized in either dollars or hours, spread over time or a sequence of program milestones. The BoE is not the estimate itself, but the methodology for arriving at the... read more
Because I Can’t Think Of A Reason It Won’t Work
A phrase often uttered as rationale for considering that a CI‘s requirements are (obviously!) met by a prospective design. This one really chaps my hide. Philosophically, it isn’t actually possible to prove the negative. Our job as Engineers is to show why it WILL work…not to challenge other people to show why it WON’T work. ... read more
Belief
A state or habit of mind in which trust, confidence, or reliance is placed in some object of perception without regard to objective proof. Because objectivity is not a criterion, belief almost always entails a significant emotional investment. Contrast with knowledge.
Bias
Literally, a leaning toward (or away from) some specific orientation. In this context, “orientation” is should be interpreted as being relative to “truth”. Being biased is the opposite of being impartial, or neutral. The term originates with reference to fabric that is cut at some angle to the weave.
Big Dog
A person who is so influential (deservedly or otherwise) that their opinions and decisions cannot be ignored. The expression appears to be most commonly used by graduates of Miss’ippi State and Georgia Tech.
Bill It As A Feature
A means of coping with an unfortunate (usually adverse) feature of a design that nevertheless leaves it compliant with the as-written requirements. “Bill” is used in the sense of a splashy advertisement for a show in hopes of distracting attention from the adverse consequences of the situation. See, for example, every other release of a... read more
Book-form
A drawing assembled in bound form. It can be A-size or larger. Even though the command media of some companies explicitly prohibits multiple volumes of a book-form drawing, some parts of said companies do it on a regular basis. These volumes are (confusingly) referred to as “sheets”…even though each page of each volume is termed “sheet”... read more
Bootstrap
In the System Engineering context, to “bootstrap” is to bring order out of chaos through the application of (perhaps) ad-hoc processes. It may, for example, be necessary to strongly tailor requirements derivation practices in order to tease out a customer’s preferences and priorities. Our typical goal is to limit such practices to a project’s “startup... read more
Bottom-up
A developmental method in which existing pieces must be integrated into a single design without regard to top-level objectives. One of two competing System Engineering theories, both of which are wrong. Contrast with Top-down.
Budget
A specific amount of resource, reserved for some specific purpose. Most of the time, the “resource” is money, and the allocation is to a WBS Element. However, the term “budget” can also be used in a technical sense, referring to some run-time resource relevant to the target system (e.g., “link budget” or “weight budget”). The... read more
Business Logic (software)
From the software engineer’s perspective, the sequences and parallel chains of steps taken by an End User to accomplish some operationally relevant task. This term may confuse some interested parties who make a distinction between “business” and some other operationally relevant aspect of their work (e.g., soldiers and engineers, to whom “business” might be a... read more