Modems

Encoding digital information into waves is referred to as modulation. Decoding digital information from waves is referred to as demodulation. Devices which do modulation and demodulation are referred to as modems. Example use cases include transmission via sound and radio waves.

Relaying

Email servers sending emails to their destinations is referred to as relaying.

Information Schema

A common standard database description view set is referred to as the information schema.

DMARC

Domain-based Message Authentication, Reporting & Conformance (DMARC) is a protocol for specifying how email receivers should utilize Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). DMARC specifications are stored in the Domain Name System (DNS).

DKIM

DomainKeys Identified Mail (DKIM) is an email digital signature system that stores public keys in the Domain Name System (DNS).

MX And SPF Records

Mail Exchange (MX) records specify email receivers. Sender Policy Framework (SPF) records specify email senders. Both are part of the Domain Name System (DNS).

MUAs, MSAs And MTAs

Clients that transfer emails to servers are referred to as mail user agents (MUAs). Servers that accept emails from clients are referred to as mail submission agents (MSAs). Servers that transfer emails to other servers are referred to as mail transfer agents (MTAs).

SMTP And Submissions Ports

Servers transfer emails using the Simple Mail Transfer Protocol (SMTP) port (25). Clients transfer emails to servers using one of the submissions ports (465 and 587).

SASL

Simple Authentication And Security Layer (SASL) is an authentication protocol. It compliments the Transport Layer Security (TLS) encryption protocol.

SQL Join Algorithm

SQL joins return subsets of all possible pairs of rows between two tables and rows of nulls. Note that subsets can be defined by inequalities as well as equalities.

Phasors

Phasors are complex exponential functions of time.  They are often used describe rotations.  Phasor multiplication is different from cross products. 

Parquet

Parquet is a tabular data encoding that includes compression and other features.

SQL Window Functions

SQL window functions are SQL functions applied to row sets associated with rows:

    window-function over (row-set-definition)

SQL Order Of Operations

For SQL select statements, with only one select operation, the order of operations is: from, join, where, group by, having, select, distinct, order by and limit.

Note that on clauses are parts of join operations, and, window functions are parts of select operations.  Note also that where operations must appear after join operations and before group by operations.

Race And Ethnicity

Race refers to physical characteristics. Ethnicity refers to cultural characteristics.

Managing Python Module Variables With Strings

Invoking the Python globals function returns a dictionary containing module information that can be modified. The dictionary keys are the module variable names as strings. The dictionary values are the module variable values.

Upserts

Upserts are database processes that update and add rows based on primary keys.

Specifying SQL Table Primary Keys Improves Performance

Specifying SQL table primary keys improves performance.

SQL Select Subexpressions

Can often use SQL select subexpressions where SQL values, lists or tables are required. SQL select subexpressions have the following form:

    (select-expression) name

SQL Common Table Expressions

Can define and use temporary SQL tables with SQL common table expressions:

    with name-1 [column-list-1] as (definition-1),
         name-2 [column-list-2] as (definition-2),
         name-3 [column-list-3] as (definition-3)