A digital single-lens reflex camera (also called a digital SLR or DSLR) is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor, as opposed to photographic film. The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens, then to a mirror that alternates to send the image to either the viewfinder or the image sensor. The traditional alternative would be to have a viewfinder with its own lens, hence the term “single lens” for this design. By using only one lens, the viewfinder of a DSLR presents an image that will not differ substantially from what is captured by the camera’s sensor. A DSLR differs from non-reflex single-lens digital cameras in that the viewfinder presents a direct optical view through the lens, rather than being captured by the camera’s image sensor and displayed by a digital screen.
DSLRs largely replaced film-based SLRs during the 2000s, and despite the rising popularity of mirrorless system cameras in the early 2010s, DSLRs remain the most common type of interchangeable lens camera in use as of 2017.
Bitcoin is a cryptocurrency and worldwide payment system. It is the first decentralized digital currency, as the system works without a central bank or single administrator. The network is peer-to-peer and transactions take place between users directly, without an intermediary. These transactions are verified by network nodes through the use of cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented by an unknown person or group of people under the name Satoshi Nakamoto and released as open-source software in 2009.
Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services. As of February 2015, over 100,000 merchants and vendors accepted bitcoin as payment. Research produced by the University of Cambridge estimates that in 2017, there are 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.
Electronic data interchange (EDI) is an electronic communication method that provides standards for exchanging data via any electronic means. By adhering to the same standard, two different companies or organizations, even in two different countries, can electronically exchange documents (such as purchase orders, invoices, shipping notices, and many others). EDI has existed for more than 30 years, and there are many EDI standards (including X12, EDIFACT, ODETTE, etc.), some of which address the needs of specific industries or regions. It also refers specifically to a family of standards. In 1996, the National Institute of Standards and Technology defined electronic data interchange as “the computer-to-computer interchange of strictly formatted messages that represent documents other than monetary instruments. EDI implies a sequence of messages between two parties, either of whom may serve as originator or recipient. The formatted data representing the documents may be transmitted from originator to recipient via telecommunications or physically transported on electronic storage media.” It distinguishes mere electronic communication or data exchange, specifying that “in EDI, the usual processing of received messages is by computer only. Human intervention in the processing of a received message is typically intended only for error conditions, for quality review, and for special situations. For example, the transmission of binary or textual data is not EDI as defined here unless the data are treated as one or more data elements of an EDI message and are not normally intended for human interpretation as part of online data processing. EDI can be formally defined as the transfer of structured data, by agreed message standards, from one computer system to another without human intervention.