on 12-Jan-2024 (Fri)

The Clean Code Blog

The Single Responsibility Principle

Web 2.0 technologies is that they facilitate collabora-
tion and sharing between users with low technical barriers

Informationssysteme sind

• offen
  • Sie interagieren mit der Umwelt und anderen Informationssystemen.
• dynamisch
  • Sie verändern sich im Zeitablauf, z.B. durch Lernprozesse.
• komplex
  • Sie verknüpfen eine große Anzahl unterschiedlicher Elemente.

Definition 1 (Informationssystem [Wikipedia]) Ein Informationssystem dient der rechnergestützten Erfassung, Speicherung, Verarbeitung, Pflege, Analyse, Benutzung, Verbreitung, Disposition, Übertragung und Anzeige von Information.

The internet as we know it doesn’t exist until much later, but internet history starts in the 1960s. In 1962, MIT computer scientist J.C.R. Licklider comes up with the idea for a global computer network. He later shares his idea with colleagues at the U.S. Department of Defense Advanced Research Projects Agency (ARPA). Work by Leonard Kleinrock, Thomas Merrill and Lawrence G. Roberts on packet-switching theory pioneers the way to the world’s first wide-area computer network. Roberts later goes on to publish a plan for the ARPANET, an ARPA-funded computer network that becomes a reality in 1969. Over the following years, the ARPANET grows.

n 1973, Robert Kahn and Vinton Cerf collaborate to develop a protocol for linking multiple networks together. This later becomes the Transmission Control Protocol/Internet Protocol (TCP/IP), a technology that links multiple networks together such that, if one network is brought down, the others do not collapse. While working at Xerox, Robert Metcalfe develops a system using cables that allows for transfer of more data over a network. He names this system Alto Aloha, but it later becomes known as Ethernet. Over the next few years, Ted Nelson proposes using hypertext to organize network information, and Unix becomes popular for TCP/IP networks. Tom Truscott and Steve Bellovin develop a Unix-based system for transferring data over phone lines via a dial-up connection. This system becomes USENET.

1980er: Dave Farber of the University of Delaware reveals a project to build an inexpensive network using dial-up phone lines. In 1982, the PhoneNet system is established and is connected to ARPANET and the first commercial network, Telenet. This broadens access to the internet and allows for email communication between multiple nations of the world. In 1981, Metcalfe’s company 3Com announces Ethernet products for both computer workstations and personal computers; this allows for the establishment of local area networks (LANs). Paul Mockapetris, Jon Postel and Craig Partridge create the Domain Name system, which uses domain names to manage the increasing number of users on the internet. In 1985, the first domain is registered: symbolics.com, a domain belonging to a computer manufacturer.

In 1990, ARPANET is decommissioned. Tim Berners-Lee and his colleagues at CERN develop hypertext markup language (HTML) and the uniform resource locator (URL), giving birth to the first incarnation of the World Wide Web. A watershed year for the internet comes in 1995: Microsoft launches Windows 95; Amazon, Yahoo and eBay all launch; Internet Explorer launches; and Java is created, allowing for animation on websites and creating a new flurry of internet activity. In 1996, Congress passes the Communications Decency Act in an effort to combat the growing amount of objectionable material on the internet. John Perry Barlow responds with an essay, A Declaration of the Independence of Cyberspace. Google is founded in 1998. In 1999, the music and video piracy controversy intensifies with the launch of Napster. The first internet virus capable of copying and sending itself to a user’s address book is discovered in 1999.

2000 sees the rise and burst of the dotcom bubble. While myriad internet-based businesses become present in everyday life, the Dow Jones industrial average also sees its biggest one-day drop in history up to that point. By 2001, most publicly traded dotcom companies are gone. It’s not all bad news, though; the 2000s see Google’s meteoric rise to domination of the search engine market. This decade also sees the rise and proliferation of Wi-Fi — wireless internet communication — as well as mobile internet devices like smartphones and, in 2005, the first-ever internet cat video.

1945 Vennevar Bush schlägt das Hypertext-System Memex vor

1990 Berners-Lee entwickelt einen Web-Client, konzipiert HTML und programmiert einen Web-Server. Er nennt das System „WorldWideWeb“. Das Telefonverzeichnis des CERN ist die erste Anwendung

1993 Die Studenten Andreesen und Bina entwickeln den Browser Mosaic

1994 Andreesen und Clark gründen die Firma Netscape

1994 Gründung des World Wide Web Consortiums W3C

1997 Tim Bray stellt die XML-Spezif kation vor

1998 Berners-Lee stellt seine Vision vom Semantischen Web vor: „Allgemeine Plattform für die Zusammenarbeit beliebiger Teilnehmer mit beliebigen Intentionen

2001 werden die Standards für das Semantischen Web entwickelt

Request-Response Zyklus in Web-Applikationen

Anfrage an den Webserver

• Hyperlink im HTML-Dokument
• Direkter Aufruf der Webseite

Request-/Response-Zyklus (HTTP-Protokoll)

• Aufbau einer TCP-Verbindung
• HTTP-Request an den in der URL spezifizierten Web-Dämon
• Zurücksenden der angeforderten Seite über die gleiche Verbindung
• Schließen der Verbindung bzw. Halten der Verbindung falls weitere Daten wie z.B. Grafiken folgen.

Darstellung der Information

• Interpretation und Darstellung des HTML-Dokuments

REST, API und JSON

REpresentational State Transfer

• ist ein Architekturstil für netzbasierte Systeme („Network-based Application Architectures“)
• Orientiert sich an Paradigmen und Verhalten des World Wide Web (HTTP-Protokoll)

Application Programming Interface

• Programmierschnittstelle
• Ressourcen-orientierte Webservices

JavaScript Object Notation

• kompaktes Datenformat
• gültiges JavaScript →eval()

Definition: Verteilte Systeme

Ein System, bei dem sich die Hardware- und Softwarekomponenten auf vernetzten Rechnern befinden und nur über den Austausch von Nachrichten kommunizieren und ihre Aktionen koordinieren. Dabei nimmt der Benutzer nur eine Ressource wahr.

Physicians, in particular, should be familiar with maculopapular rashes associated with EM and SJS/TEN.

Maculopapular rashes (see Table 57.1) (Fig. 57.1) are usually seen in a range of illnesses, including those due to viruses, bacteria, fungi, drug eruptions, and immune complex–mediated syndromes.

EM and its variants may be considered a special category of macu- lopapular rash. EM is an uncommon acute, immune-mediated, self- limited, usually mild mucocutaneous syndrome that is often relapsing.71,72,73 The disease is usually related to an acute infection, most commonly a recurrent HSV infection. It is uncommonly related to drug ingestion (i.e., <0%)

The following classification of EM is based on that provided by Bastuji-Garin and colleagues.73,74 Subtypes of EM include (1) EM major: skin lesions with involvement of mucous membranes, (2) EM minor: skin lesions without involvement of mucous membranes, (3) herpes- associated EM, and (4) mucosal EM (Fuchs syndrome): mucous membrane lesions without cutaneous involvement.

Further, the epidemiology of EM differs from SJS/TEN because patients with EM are younger, are more often male, have frequent recurrences, have less fever, have milder mucosal lesions, and lack association with collagen vascular diseases, HIV infection, or cancer.76

Target lesions are the hallmark of EM. The skin eruption generally arises abruptly; most commonly all lesions appear within 3 to 5 days and resolve in approximately 2 weeks. Initially, lesions may begin as round erythematous papules that evolve into classic target lesions.

Typical target lesions consist of three components: a dusky central area or blister, a dark red inflammatory zone surrounded by a pale ring of edema, and an erythematous halo on the extreme edge of the lesion. Although there are often a limited number of lesions, in some cases hundreds may form.

Most lesions occur in a symmetrical, acral distribution on the extensor surfaces of the extremities (hands and feet, elbows, and knees), face and neck, and, less commonly, thighs, buttocks, and trunk. They often appear acrally and then spread in a centripetal manner.

Although the lesions are usually asymptomatic, patients occasionally report burning or itching.

Mucous membrane (≈70% oral, ≈25% genital, ≈15% ocular) involvement usually accompanies the cutaneous lesions, although patients may present only with mucous membrane involvement.77

Although many factors (e.g., infections, medications, malignancy, autoimmune disease, immunizations, sarcoidosis, and radiation) have been linked to EM, infections account for approximately 90% of cases. HSV has been the infection most commonly linked to EM (≈80% of infectious cases),78,79 but Mycoplasma pneumoniae is an important cause of EM (≈5%–10% of infectious cases), especially in children.80

The differential diagnosis of target-appearing skin lesions has been reviewed and includes EM, SJS, TEN, ecthyma gangrenosum, syphilis, fixed-drug eruption, contact dermatitis, vasculitis, acute connective tissue diseases, and autoimmune blistering diseases.81

SJS and TEN are acute, life-threatening mucocutaneous reactions characterized by extensive necrosis and detachment of the epidermis.82–87 Although TEN is rare, with an incidence of approximately two cases per million population per year, it is a devastating disease with a mortality rate of 30% to 50%.

Owing to the similarity in clinical and histologic findings, risk factors, drug causality, and mechanisms, these two syn- dromes are considered severity variants of an identical process that differs only in the final extent of body surface involved.87 TEN involves sloughing of greater than 30% of the body surface, whereas SJS involves less than 10% of the total body surface; total body surface area involve- ment between 10% and 30% is known as SJS-TEN overlap

SJS and TEN typically have a prodrome of fever and flulike symptoms beginning 1 to 3 days before the development of skin lesions. These may be accompanied by skin tenderness and photophobia. Both SJS and TEN are characterized by rapidly expanding, often irregular macules (“atypical target lesions”) and involvement of more than one mucosal site (oral, conjunctival, and anogenital).

A majority of cases in adults are drug induced; medications cause 30% to 50% of cases of SJS and up to 80% of cases of TEN.

Petechiae are the most common skin and mucous membrane lesions observed in endocarditis, occurring in 20% to 40% of patients. The lesions are small, flat, and reddish brown and do not blanch on pressure. The petechiae may be observed on the skin, especially on the heels, shoulders, and legs. Mucous membrane (oral and conjunctiva) involve- ment is common. Petechiae frequently occur in small crops. Lesions usually are transient.

Recent series suggests that they are now present in less than 10% of patients with endocarditis because endocarditis is now diagnosed more rapidly before the development of Osler nodes. These lesions are tender, indurated, erythematous nodules, with a pale center that is 1.0 to 1.5 mm in diameter.166–168 Osler nodes most commonly occur on the pads of the fingers or toes but may also occur on the thenar and hypothenar eminences and over the arms. Pain may be elicited by palpating the tips of the digits. Osler nodes tend to occur in crops, are rarely numerous, and tend to be transient. The lesions usually resolve without necrosis or suppuration 1 to 3 days after antibiotic therapy is initiated.

Histologically, Osler nodes show microabscesses with microemboli in adjacent arterioles. Osler nodes are most commonly associated with subacute bacterial endocarditis due to infection with streptococci but may occur in endocarditis due to infection with fungi or gram-negative bacilli or in systemic lupus erythematosus, typhoid fever, and gonococcemia. Osler nodes probably represent the sequelae of vascular occlusion by microemboli leading to localized vasculitis.169

Janeway lesions consist of small erythematous macules or, less commonly, small nodular hemorrhages in the palms and soles. Although they may be seen in subacute bacterial endocarditis, they are more common in acute endocarditis, especially that due to S. aureus. Unlike Osler nodes, Janeway lesions are painless. Histologically, they show microabscesses with neutrophil infiltration of capillaries.