Friday, August 3, 2012

Table (database)

In relational databases and flat file databases, a table is a set of data elements (values) that is organized using a model of verticalcolumns (which are identified by their name) and horizontal rows, the cell being the unit where a row and column intersect.^[1] A table has a specified number of columns, but can have any number of rows^{[citation needed]}. Each row is identified by the values appearing in a particular column subset which has been identified as a unique key index.

Table is another term for relations; although there is the difference in that a table is usually a multi-set (bag) of rows whereas a relation is a set and does not allow duplicates. Besides the actual data rows, tables generally have associated with them some meta-information, such as constraints on the table or on the values within particular columns.

The data in a table does not have to be physically stored in the database. Views are also relational tables, but their data are calculated at query time. Another example are nicknames, which represent a pointer to a table in another database.

Comparisons with other data structures

In non-relational systems, hierarchical databases, the distant counterpart of a table is a structured file, representing the rows of a table in each record of the file and each column in a record.

Unlike a spreadsheet, the datatype of field is ordinarily defined by the schema describing the table. Some relational systems are less strict about field datatype definitions.

[edit]Tables versus relations

In terms of the relational model of databases, a table can be considered a convenient representation of a relation, but the two are not strictly equivalent. For instance, an SQL table can potentially contain duplicate rows, whereas a true relation cannot contain duplicatetuples. Similarly, representation as a table implies a particular ordering to the rows and columns, whereas a relation is explicitly unordered. However, the database system does not guarantee any ordering of the rows unless an ORDER BY clause is specified in theSELECT statement that queries the table.

An equally valid representations of a relation is as an n-dimensional chart, where n is the number of attributes (a table's columns). For example, a relation with two attributes and three values can be represented as a table with two columns and three rows, or as a two-dimensional graph with three points. The table and graph representations are only equivalent if the ordering of rows is not significant, and the table has no duplicate rows.

[edit]Table types

Two types of tables exist.

A relational table, which is the basic structure to hold user data in a relational database.
An object table, which is a table that uses an object type to define a column. It is defined to hold instances of objects of a defined type.

Excel Charts

In Excel, you can create charts. A chart is a graphical representation of numbers. This tutorial teaches you how to create a chart in Excel.

Lesson 4: Creating Charts

In Microsoft Excel, you can represent numbers in a chart. On the Insert tab, you can choose from a variety of chart types, including column, line, pie, bar, area, and scatter. The basic procedure for creating a chart is the same no matter what type of chart you choose. As you change your data, your chart will automatically update.
You select a chart type by choosing an option from the Insert tab's Chart group. After you choose a chart type, such as column, line, or bar, you choose a chart sub-type. For example, after you choose Column Chart, you can choose to have your chart represented as a two-dimensional chart, a three-dimensional chart, a cylinder chart, a cone chart, or a pyramid chart. There are further sub-types within each of these categories. As you roll your mouse pointer over each option, Excel supplies a brief description of each chart sub-type.

Create a Chart

To create the column chart shown above, start by creating the worksheet below exactly as shown.

After you have created the worksheet, you are ready to create your chart.

EXERCISE 1

Create a Column Chart

.

Select cells A3 to D6. You must select all the cells containing the data you want in your chart. You should also include the data labels.
Choose the Insert tab.
Click the Column button in the Charts group. A list of column chart sub-types types appears.
Click the Clustered Column chart sub-type. Excel creates a Clustered Column chart and the Chart Tools context tabs appear.

Apply a Chart Layout

Context tabs are tabs that only appear when you need them. Called Chart Tools, there are three chart context tabs: Design, Layout, and Format. The tabs become available when you create a new chart or when you click on a chart. You can use these tabs to customize your chart.

You can determine what your chart displays by choosing a layout. For example, the layout you choose determines whether your chart displays a title, where the title displays, whether your chart has a legend, where the legend displays, whether the chart has axis labels and so on. Excel provides several layouts from which you can choose.

EXERCISE 2

Apply a Chart Layout

Click your chart. The Chart Tools become available.
Choose the Design tab.
Click the Quick Layout button in the Chart Layout group. A list of chart layouts appears.
Click Layout 5. Excel applies the layout to your chart.

Add Labels

When you apply a layout, Excel may create areas where you can insert labels. You use labels to give your chart a title or to label your axes. When you applied layout 5, Excel created label areas for a title and for the vertical axis.

EXERCISE 3

Add labels


Before	After

Select Chart Title. Click on Chart Title and then place your cursor before the C in Chart and hold down the Shift key while you use the right arrow key to highlight the words Chart Title.
Type Toy Sales. Excel adds your title.
Select Axis Title. Click on Axis Title. Place your cursor before the A in Axis. Hold down the Shift key while you use the right arrow key to highlight the words Axis Title.
Type Sales. Excel labels the axis.
Click anywhere on the chart to end your entry.

Switch Data

If you want to change what displays in your chart, you can switch from row data to column data and vice versa.

EXERCISE 4

Switch Data


Before	After

Click your chart. The Chart Tools become available.
Choose the Design tab.
Click the Switch Row/Column button in the Data group. Excel changes the data in your chart.

Change the Style of a Chart

A style is a set of formatting options. You can use a style to change the color and format of your chart. Excel 2007 has several predefined styles that you can use. They are numbered from left to right, starting with 1, which is located in the upper-left corner.

EXERCISE 5

Change the Style of a Chart

Click your chart. The Chart Tools become available.
Choose the Design tab.
Click the More button in the Chart Styles group. The chart styles appear.

Click Style 42. Excel applies the style to your chart.

Change the Size and Position of a Chart

When you click a chart, handles appear on the right and left sides, the top and bottom, and the corners of the chart. You can drag the handles on the top and bottom of the chart to increase or decrease the height of the chart. You can drag the handles on the left and right sides to increase or decrease the width of the chart. You can drag the handles on the corners to increase or decrease the size of the chart proportionally. You can change the position of a chart by clicking on an unused area of the chart and dragging.

EXERCISE 6

Change the Size and Position of a Chart

Use the handles to adjust the size of your chart.
Click an unused portion of the chart and drag to position the chart beside the data.

Move a Chart to a Chart Sheet

By default, when you create a chart, Excel embeds the chart in the active worksheet. However, you can move a chart to another worksheet or to a chart sheet. A chart sheet is a sheet dedicated to a particular chart. By default Excel names each chart sheet sequentially, starting with Chart1. You can change the name.

EXERCISE 7

Move a Chart to a Chart Sheet

Click your chart. The Chart Tools become available.
Choose the Design tab.
Click the Move Chart button in the Location group. The Move Chart dialog box appears.

Click the New Sheet radio button.
Type Toy Sales to name the chart sheet. Excel creates a chart sheet named Toy Sales and places your chart on it.

Change the Chart Type

Any change you can make to a chart that is embedded in a worksheet, you can also make to a chart sheet. For example, you can change the chart type from a column chart to a bar chart.

EXERCISE 8

Change the Chart Type

Click your chart. The Chart Tools become available.
Choose the Design tab.
Click Change Chart Type in the Type group. The Chart Type dialog box appears.
Click Bar.
Click Clustered Horizontal Cylinder.
Click OK. Excel changes your chart type.

Chart

For other uses, see Chart (disambiguation) , Graph (disambiguation) , and Diagram

For information about charts in Wikipedia, see Wikipedia:Graphs and charts.

A pie chart.

A chart is a graphical representation of data, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart".^[1] A chart can represent tabular numeric data, functions or some kinds of qualitative structures.

The term "chart" as a graphical representation of data has multiple meanings:

A data chart is a type of diagram or graph, that organizes and represents a set of numerical or qualitative data.
Maps that are adorned with extra information for some specific purpose are often known as charts, such as a nautical chart or aeronautical chart.
Other domain specific constructs are sometimes called charts, such as the chord chart in music notation or a record chart for album popularity.

Charts are often used to ease understanding of large quantities of data and the relationships between parts of the data. Charts can usually be read more quickly than the raw data that they are produced from. They are used in a wide variety of fields, and can be created by hand (often on graph paper) or by computer using a charting application. Certain types of charts are more useful for presenting a given data set than others. For example, data that presents percentages in different groups (such as "satisfied, not satisfied, unsure") are often displayed in apie chart, but may be more easily understood when presented in a horizontal bar chart.^[2] On the other hand, data that represents numbers that change over a period of time (such as "annual revenue from 1990 to 2000") might be best shown as a line chart.

Features of a chart

A chart can take a large variety ; however, there are common features that provide the chart with its ability to extract meaning from data.

Typically a chart is graphical, containing very little text, since humans are generally able to infer meaning from pictures quicker than from text. One of the more important uses of text in a graph is in the title. A graph's title usually appears above the main graphic and provides a succinct description of what the data in the graph refers to.

Dimensions in the data are often displayed on axes. If a horizontal and a vertical axis are used, they are usually referred to as the x-axis and y-axis respectively. Each axis will have a scale, denoted by periodic graduations and usually accompanied by numerical or categorical indications. Each axis will typically also have a label displayed outside or beside it, briefly describing the dimension represented. If the scale is numerical, the label will often be suffixed with the unit of that scale in parentheses. For example, "Distance traveled (m)" is a typical x-axis label and would mean that the distance travelled in metres is related to the horizontal position of the data.

Within the graph a grid of lines may appear to aid in the visual alignment of data. The grid can be enhanced by visually emphasizing the lines at regular or significant graduations. The emphasized lines are then called major grid lines and the rest of the grid lines are minor grid lines.

The data of a chart can appear in all manner of formats, with or without individual labels. It may appear as dots or shapes, connected or unconnected, and in any combination of colors and patterns. Inferences or points of interest can be overlayed directly on the graph to further aid information extraction.

When the data appearing in a chart contains multiple variables, the chart may include a legend. A legend contains a list of the variables appearing in the chart and an example of their appearance. This information allows the data from each variable to be identified in the chart.

[edit]Types of charts

[edit]Common charts

Four of the most common charts are:

This gallery shows:

A histogram consists of tabular frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to the frequency of the observations in the interval.
A bar chart is a chart with rectangular bars with lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally.
A pie chart shows percentage values as a slice of a pie.
A line chart is a two-dimensional scatterplot of ordered observations where the observations are connected following their order.

Other common charts are:

[edit]Less-common charts

Examples of less common charts are:

This gallery shows:

A bubble chart is a two-dimensional scatterplot where a third variable is represented by the size of the points.
A Polar area diagram, sometimes called a Coxcomb chart, is an enhanced form of pie chart developed by Florence Nightingale.
A radar chart or "spider chart" is a two-dimensional chart of three or more quantitative variables represented on axes starting from the same point.
A waterfall chart also known as a "Walk" chart, is a special type of floating-column chart.
A Tree Map where the areas of the rectangles correspond to values. Other dimensions can be represented with colour or hue.
A streamgraph, a stacked, curvilinear area graph displaced around a central axis

[edit]Field-specific charts

Some types of charts have specific uses in a certain field

This gallery shows:

Stock market prices are often depicted with a open-high-low-close chart with a traditional bar chart of volume at the bottom.
Candlestick charts are another type of bar chart used to describe price movements of an equity over time.
A Kagi chart is a time-independent stock tracking chart that attempts to minimise noise.
Alternatively, where less detail is required, and chart size is paramount, a Sparkline may be used.

Other examples:

Interest rates, temperatures, etc., at the close of the period are plotted with a line chart.
Project planners use a Gantt chart to show the timing of tasks as they occur over time.

[edit]Well-known named charts

Some of the better-known named charts are:

Some specific charts have become well known by effectively explaining a phenomenon or idea.

An Allele chart is a chart originating from the study of genetics to show the interaction of two data points in a grid.
A Gantt chart helps in scheduling complex projects.
The Nolan chart and the Pournelle chart classify political philosophies according to two axes of variation.
A PERT chart is often used in project management.
The Smith chart serves in radio electronics.

[edit]Other charts

There are dozens of other types of charts. Here are some of them:

[edit]Common plots

Main article: Plot (graphics)