Information Management

1. Secure
2. Rapidly accessible

1. May be hard to share
2. More expensive
3. You have to deal with migrating the information when upgrading to new devices.

1. Tends to be cheaper than personal devices on a per gigabyte measure.
2. Easier to share with others or to use your information on multiple personal devices.

1. May be less secure, both because the data is available over the network and hence is subject to attacks by hackers and because the data may be requisitioned by governments.
2. Access may be less rapid because it is over the network and may even be unavailable when you do not have network access.

1. Tries to drop information that is considered less significant. For example, image compression tries to drop color information that can't be detected by the human eye
2. Repeatedly saving an image in a lossy format will progressively degrade the data quality

1. Codec: The algorithm used for encoding/decoding the data. The encoding often involves some type of compression.
2. Container: The file(s) holding the data produced by the codec.

1. Advantage: Compact--characters take only 1 byte
2. Disadvantage: Only encodes English character and punctuation set.

1. Standard
   1. defines a codespace of 1,114,112 codepoints in the range 0x0 to 0x10FFFF. The standard uses codepoint rather than "character" because a code point could be a character or grapheme.
   2. The first 128 codepoints are identical to the 128 Ascii character codes.
2. Encoding: Various standards are used to encode Unicode characters. The simplest encoding is to simply use 4 bytes (although 3 would suffice) but this is wasteful since the codepoints for the most commonly used characters only require 1-2 bytes.
   1. UTF-8: The most common encoding, which is used for most web-pages, html, XML, etc. It can represent a character code using 1-4 bytes. The first bits of the first byte allows the remaining bytes to be decoded (x's denote the bits used for the character code):
      1. 1 byte: The encoding is 0xxxxxxx
      2. 2 bytes: The encoding is 110xxxxx 10xxxxxx
      3. 3 bytes: The encoding is

         1110xxxx 	10xxxxxx 	10xxxxxx
         			      

      4. 4 bytes: The encoding is

         11110xxx 	10xxxxxx 	10xxxxxx 	10xxxxxx	
         			      

      Notice how the start of the first byte always allows a decoder to determine how many bytes will be used to encode this character code. Note that all Ascii codes can be encoded in a single byte, which is much more compact than using 4 bytes.
   2. UTF-16: Uses 1 or 2 16-bit (i.e., 2 byte) code units to denote Unicode character codes. Used internally in Windows, Java, and Javascript but never caught on as an encoding for web pages.
   3. UTF-32: The simple 32 bit encoding of a unicode character. It is very time efficient because it requires no decoding but is very space inefficient and hence is rarely used.

1. All computations required to create the document have already been performed. The document is in its final printable format. As a result pdf documents originally were not meant to be modified once created.
2. More recent pdf documents have type-in text boxes or other types of widgets that allow small changes to be made once the file has been created.

1. Most widely used document format for the web
2. Cascading style sheets (css) are used to specify the presentation of the document
3. Easily modified with a text editor
4. HTML documents are meant to be displayed in a browser and not printed. CSS does not support page layout algorithms for HTML, which makes HTML a poor choice for printed documents.

{
  "name" : "brad",
  "age": 54,
  "hobbies": ["hiking","climbing","bridge","golf","travel"]
}
		

1. Most widely used format for documents that need to be edited and then printed.

1. RTF is typically not a final format for a document but an intermediate format that is used to transfer the document to a new platform, such as from Microsoft Word to OpenOffice or Apple Pages

1. HTML is an XML-based format
2. Can be rendered into many forms, either printable or browsable, using XSL (Extensible Stylesheet Language)
3. RSS (Rich Site Summary) is a common format used by news organizations to organize and store news content
4. Many hope that it will become the future standard for technical file formats (source is wikipedia), but I have my doubts. XML seemed to be more popular a few years back, but I do not hear about it as much any more. XML is indeed flexible as a way of specifying arbitrary document formats that can be type-checked and parsed, but it is also heavy-weight and cumbersome. JSON seems to be supplanting it as the preferred format for storing and transmitting data.

1. The different between a postscript file and a pdf file is that the postscript file is not in its finished form while a pdf file is.
2. postscript was developed when CPU's were much slower and printing would waste valuable CPU time. Printers were equipped with CPU's that could interpret postscript programs and thus offload the computation from CPU's. As CPU's became much more powerful, it became unnecessary to offload the print computations and postscript has been largely relegated to legacy code.

1. .csv (comma separated values): An intermediate format, much like RTF, but used for transferring spreadsheet style data to different platforms

1. Compression
2. Color Model
   1. Bitmap: 1 bit per pixel which is either on or off. Good for black and white images
   2. Gray-Scale: Several bits per image indicating a shade of grayness between white and black. NeXT was an early example of a gray-scale system.
   3. Full Color: Bits are used to specify color values for red, green, and blue. The combination of these color values produces the desired color. Most existing systems allow 8 bits per color for a total of 3 bytes per color.
   4. Color Map: Color values are an index into a table of fully specified (i.e. 24 bit) colors. Typically 8 bits are allocated for the color value giving a possibility of 256 colors.

1. JPEG: A lossy, full color compression format that was designed for storing photographs. Not good for storing graphics since the lossiness causes the graphics to look too bitmappy (e.g., a smooth line may look jagged)
2. GIF: An older lossless, color map, compression format that was designed for storing graphics. The patent for GIF was held for many years by CompuServe, its developer.
   1. Not good for storing photographs because of the limited colors a gif file can store.
   2. Can created animated GIF files that perform animations using multiple images.
   3. Not good for graphics involving color gradations because of the limited colors available. It's typically best to have shapes with solid colors.
3. PNG: A newer, open source replacement for GIF developed in part to avoid paying fees to CompuServe for its GIF format. It is a full color, lossless compression format for storing images. It produces larger files than jpeg files so it is not frequently used for storing photographs.
   1. Good for storing graphics files, just like GIF
   2. It is a good format to use for storing screenshots, which involve a mix of images and text (note that screenshots have a much lower resolution than photos so the files will not be overly large).
4. TIFF: A non-compressed, lossless, full color format that is good for storing documents or photos while they are being processed using software.
   1. TIFF images create very large files because they are uncompressed and lossless.
   2. TIFF files are good for storing multiple-page documents
   3. TIFF files are also good for storing photos or documents while they are being processed by photo or page layout software. The output can be stored in more compact formats, such as jpeg or pdf.

1. security: prevents unauthorized users from accessing the database
2. integrity: maintains the consistency of stored data (e.g., a person's salary will not appear differently in two different parts of the database).
3. concurrency: allows multiple users to use the database simultaneously, without introducing integrity problems
4. recovery control: restores the database to a previous consistent state following a hardware or software failure
5. user-accessible catalog: contains descriptions of the data in the database
6. views: allows each user to have an individualized view of the database
   1. provide security: can limit fields that are accessable by certain classes of users
   2. customization: fields can be given names that are more meaningful for a certain group of users
   3. data abstraction: hides changes to the database that do not affect the data presented by this view
   4. reduces complexity: users only needs to know about data that they care about

1. Seek time: time to move mechanical read/write arm to the appropriate track
2. Rotational latency: time for appropriate sector of track to rotate under the read/write arm
3. 2017 seek times (source: wikipedia): Random access times have not improved significantly in recent years
   1. 3-4 ms for high end (3000-4000 microseconds)
   2. 9 ms for average desk top
   3. 12-15 ms for average mobile device or laptop

4. 2017 rotational latency times: 2-7.15ms (source: wikipedia)
5. 2017 transfer rates:
   1. consumer grade hard disk drive: 200 MB/second for both read and write (source: User Benchmark).
   2. enterprise grade hard disk drive: 200-300MB/second for both read and write (source: Tom's IT Pro).

1. Cost: About 24 cents per gigabyte in 2017, which is about 4 times the cost of a gigabyte for a hard disk drive.
2. Access times for Solid State Device (SSD) (source: wikipedia).
   1. < 0.1ms seek time (no latency because no rotation)
   2. transfer rates
      1. 200-2500MB per second
      2. write times for less expensive SSD's can be 10 times slower than read rates (writes require more energy because they need to flip the polarity of a bit, which means enough energy to overcome the current polarity and reverse it).
      3. write times for higher end SSD's is comparable to read times

1. Primary Index: File is physically clustered using the primary key
2. Cluster Index: File is physically clustered on a key other than the primary key--Often you do not cluster on the primary key if it is an artificial key since an artificial key is unlikely to be used in range queries
   1. Importance of a cluster key: improves performance of range queries (e.g., find all people who were hired between Jan. 1, 2018 and Dec. 31, 2018).
3. Secondary Index: Index on a non-clustered attribute(s) that helps the query optimizer more efficienty locate records
   1. Secondary indices are good for point queries that ask for a single value (e.g., find all peiple who were hired on Feb. 1, 2018).

1. Entities are relations
2. Relationships may be represented as relations or foreign keys (more on this when we talk about databases)

1. Entities are typically rows or columns
2. Relationships are the cells (e.g, Brad scored a 95 on the midterm) or equations among attributes

1. Entities are the web-pages
2. Relationships are the links

1. 20-30 frames per second is required to gain the illusion of smooth, continuous motion. Since human perception varies, 30 frames per second is the figure to shoot for.
2. 5 frames per second is the lower acceptable bound for dragging interactions
3. Non-continuous interactions
   1. 1-2 second delays are acceptable for retrieving information or finding information in a document
   2. After 10-15 seconds the illusion of interactivity is lost
   3. Percent-done indicators or some other indicator that gives an estimate of remaining time or at least an indication that something is happening are useful when a delay is necessary

1. Human retina can only distinguish about 64-128 shades of hue (a hue is a single color)

   ==> we can represent all of the colors that can be sensed by the retina using 6-7 bits for each primary color

2. Human ocular system can sense somewhat more shades. 256 levels of shade for each primary color is more than adequate for human visual needs which is why computer displays represent colors with 24 bits.
3. Humans are 10 times more sensitive to variations in intensity than they are to variations in hue or the color wavelength of light (this has been shown experimentally but follows from the greater number of rods than cones and the fact that rods are far more sensitive to intensity than cones).

   ==> contrasting intensities of colors should be carefully considered when superimposing colors on a display (e.g., dark on light or vice versa works well).

4. Humans are much less capable of distinguishing intensity at the fringes of the spectrum (deep red and violet) than in the center where the yellows and greens are found.

   ==> The reds and blues are harder for the eye to resolve than greens and yellows

5. About 1% of the population is color blind to one or more of the primary colors--this does not affect the ability to sense intensity.

   ==> discrimination of colors should *not* be based solely on hue--also use intensity to discriminate colors

1. only have one animation running at a time
2. use animation to attract the eye to a particular part of the display but then pause the animation if the animation is not required in order for the user to understand the presentation.

1. This is the model for generated light, such as from the sun or from a computer screen.
2. This model is used most often by drawing packages

1. Hue = primary wavelength of light
2. Saturation = pureness of the primary wavelength-high saturation means a relatively pure color whereas low saturation means a lot of white or gray is mixed in
3. Value = intensity or brightness
4. This model is what most "ordinary" people are used to.

1. This is the model for reflected light, such as from a printed document or a painting.
2. Each color corresponds to the absence of one of the additive primaries (since light is reflected, the color is what the eye sees after one of the additive primaries has been absorbed by the reflective surface).

   Example: Cyan is the absence of red, magenta is the absence of green, and yellow is the absence of blue

3. This model is most familiar to people in the visual arts and is used by printers

1. Examples are Times New Roman and Cambria.
2. The curly decorations help characters blend together, which makes them ideal for high resolution devices, such as printers. Hence serif fonts are more commonly used in printed documents.

1. Examples are Helvetica, Arial, and Calibri
2. The lack of serifs provide good distinction between characters, which can prevent blurriness on low resolution devices, such as some computer screens. Hence sans serif fonts are more commonly used on computer screens, and should be used in preference to serif fonts on computer screens because you cannot guarantee that your output will be viewed on a high resolution screen.

1. Fonts where each character has a fixed width.
2. A common example is Courier
3. Typically used to represent code in either printed documents or on a computer screen.
4. Typewriter fonts are less aesthetically appealing than serif or sans-serif fonts, so they are rarely used outside of presenting computer code.