User’s Guide : EViews Fundamentals : Object Basics : What is an Object?
What is an Object?
Object Data
Object Views
Object Procedures
Object Types
Information in EViews is stored in objects. Each object consists of a collection of information related to a particular area of analysis. For example, a series object is a collection of information related to a set of observations on a particular variable. An equation object is a collection of information related to the relationship between a collection of variables.
Note that an object need not contain only one type of information. For example, an estimated equation object contains not only the coefficients obtained from estimation of the equation, but also a description of the specification, the variance-covariance matrix of the coefficient estimates, and a variety of statistics associated with the estimates.
Associated with each type of object is a set of views and procedures which can be used with the information contained in the object. This association of views and procedures with the type of data contained in the object is what we term the object oriented design of EViews.
The object oriented design simplifies your work in EViews by organizing information as you work. For example, since an equation object contains all of the information relevant to an estimated relationship, you can move freely between a variety of equation specifications simply by working with different equation objects. You can examine results, perform hypothesis and specification tests, or generate forecasts at any time. Managing your work is simplified since only a single object is used to work with an entire collection of data and results.
This brief discussion provides only the barest introduction to the use of objects. The remainder of this section will provide a more general description of EViews objects. Subsequent chapters will discuss series, equations, and other object types in considerable detail.
Object Data
Each object contains various types of information. For example, series, matrix, vector, and scalar objects, all contain mostly numeric information. In contrast, equations and systems contain complete information about the specification of the equation or system, and the estimation results, as well as references to the underlying data used to construct the estimates. Graphs and tables contain numeric, text, and formatting information.
Since objects contain various kinds of data, you will want to work with different objects in different ways. For example, you might wish to compute summary statistics for the observations in a series, or you may want to perform forecasts based upon the results of an equation. EViews understands these differences and provides you with custom tools, called views and procedures, for working with an object’s data.
Object Views
There is more than one way to examine the data in an object. Views are tabular and graphical windows that provide various ways of looking at the data in an object.
For example, a series object has a spreadsheet view, which shows the raw data, a line graph view, a bar graph view, a histogram-and-statistics view, and a correlogram view. Other views of a series include distributional plots, QQ-plots, and kernel density plots. Series views also allow you to compute simple hypothesis tests and statistics for various subgroups of your sample.
An equation object has a representation view showing the equation specification, an output view containing estimation results, an actual-fitted-residual view containing plots of fitted values and residuals, a covariance view containing the estimated coefficient covariance matrix, and various views for specification and parameter tests.
Views of an object are displayed in the object’s window. Only one window can be opened for each object and each window displays only a single view of the object at a time. You can change views of an object using the View menu located in the object window’s toolbar or the EViews main menu.
Perhaps the most important thing to remember about views is that views normally do not change data outside the object. Indeed, in most cases, changing views only changes the display format for the data, and not the data in the object itself.
Object Procedures
Most EViews objects also have procedures, or procs. Like views, procedures often display tables or graphs in the object’s window. Unlike views, however, procedures alter data, either in the object itself or in another object.
Many procedures create new objects. For example, a series object contains procedures for smoothing or seasonally adjusting time series data and creating a new series containing the smoothed or adjusted data. Equation objects contain procedures for generating new series containing the residuals, fitted values, or forecasts from the estimated equation.
You select procedures from the Proc menu on the object’s toolbar or from the EViews main menu.
Object Types
The most common objects in EViews are series and equation objects. There are, however, a number of different types of objects, each of which serves a unique function. Most objects are represented by a unique icon which is displayed in the object container (workfile or database) window. The basic object icons are given by:
Despite the fact that they are also objects, object containers do not have icons since they cannot be placed in other object containers—thus, workfiles and databases do not have icons since they cannot be placed in other workfiles or databases.
Note also that there are special icons that correspond to special versions of the objects:
Auto-updating Series
Group data and definitions (in databases)
Undefined Link
If you set a series object to be auto-updating (see “Auto-Updating Series”), EViews will use the special icon to indicate that the series depends upon a formula. In contrast, an auto-updating alpha series (which we imagine to be less common) uses the original alpha icon, with an orange color to indicate the presence of a formula.
When group data are stored in databases, you will be given the option of storing the group definition (list of series names) alone, or both the group definition and the series contained in the group (see “Store, Fetch, and Copy of Group Objects”). If the latter are stored, the standard group icon will be modified, with the “+” indicating the additional presence of the series data.
Lastly, a link object (see “Series Links”), is always in one of three states, depending upon the definition contained in the link. If the link is to a numeric source series, the link object is displayed using a series icon, since it may be used as though it were an ordinary series, with a distinctive pink color used to indicate that the object depends on linked data. If the link is to an alpha source series, the link will show up as an alpha series icon, again in pink. If, however, the link object is unable to locate the source series, EViews will display the “?” icon indicating that the series type is unknown.