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ISAT 426 Exam #1 pt3
Terms in this set (31)
What are the foundations of modeling?
•Models are simplifications of real systems
•They help us to understand the behavior of these systems by focusing on what (we believe) is important
•They can be used both to explain the past and to predict the future
They are often based on observation
What is an example of modeling?
•Isaac Newton observed the motion of objects in response to force, and found he could describe this behavior with F = ma.
•This is a mathematical model (though physicists glorify it by calling it a "law").
•It correctly describes past behaviors and predicts future ones...
...but only under some conditions!
What are the kinds of models?
-mathematical (F = ma)
-physical (a stream flow)
-mental (expectations of future behavior)
How do we approach modeling (the steps)?
1. Define the system
2. Draw a system diagram
3. Enumerate relationships
4. Determine the units for variables and parameters/coefficients
1. Define the system
•Flux (flows across boundaries)
•Time frame under consideration
•Temporal and spatial resolution
•Scope (what's included, what's excluded)
2. Draw a system diagram
•A diagram will help you understand your conceptual model of the system and explain it to others
•Doesn't have to be art - but should be clear
3. Enumerate relationships
•Graphical relationships (e.g. spatial associations)
•Other relationships, e.g.
Economic (could be mathematical)
4. Determine the units
•Mathematical models will generally consist of variables and coefficients (or parameters).
•Units of measurement must be determined, and should be analyzed for consistency BEFORE any calculations are performed.
•While the variables will be either manipulated (independent) or recorded (dependent), coefficients/parameters must be set.
•This calibration process involves using real data from past observations.
•The coefficients are adjusted so that the model output matches the observed system output.
•Once the model is calibrated, we validate it by using a different set of real data.
•This time the model coefficients are not changed, and model output is compared to the observed system output.
•Models need to be documented in order to be given credibility
•All of the above need to be included in the documentation
•The most important things to document are your assumptions
What are some characteristics of environmental models?
-Overshoot & Collapse
What is a database?
-An organized, machine-readable collection of symbols, to be interpreted as a true account of some enterprise.
-A database is typically available to a community of users, with possibly varying requirements.
What are databases as collections of objects?
A relational database holds a set of "objects" of different types:
What do the database objects do?
•Tables contain the actual data
•Forms simplify entering and viewing data
•Queries let you view parts of the data
•Reports format and print selected data
•Macros let you automate command sequences
What are tables as database objects?
•One database can hold many tables
•The tables hold different kinds of data
•Data can be linked between tables
•The link between tables is a RELATION
What is a relational database?
A database whose symbols are organised into a collection of relations.
What is related?
•We say the two TABLES are "related"
•We really mean certain RECORDS in the two tables are related
•The ability to relate records in multiple tables gives relational databases their power
How do you use relations?
•Linked records can be ENTERED using a data entry form that combines tables and automates the linkage
•Linked records can be viewed together in queries that show only what you want
•Linked records can be combined in reports
What are the characteristic of a relation (table)?
-Two-dimensional structure with rows and columns
-A relation represent a single entity
-Each table must have an attribute to uniquely identify each row
-Column values all have same data type
-Order of the rows and columns is immaterial to the DBMS
What are the properties of a relation?
1. There are no duplicate tuples (rows)
2. Tuples (rows) are unordered (top to bottom).
3. Attributes (columns) are unordered (left to right).
4. All attribute values are atomic.
What is a primary key?
•A PK is an attribute, or collection of attributes, whose values uniquely identify each tuple in a relation.
•To be unique, a PK must be minimal (contain no unnecessary attributes)
and mustnot change in value.
•One attribute, or collection of attributes, that can serve as a PK is called candidate key,
•And the remaining keys that cannot be used as a PK are called alternate key.
What is the entity integrity rule?
•Guarantees that each entity will have a unique identity and ensures that foreign key values can properly reference primary key values.
-No component of the primary key is allowed to accept nulls.
-By "null" here, we mean that information is missing for some reason.
How do you combine data entry form?
•Main form holds main table data
-form displays one main record at a time
•Embedded sub-forms hold sub-table data
-form displays multiple records in datasheet view
•Lookup table embedded on form
-as a dropdown box or scrolling list
-view the code names on the list
-click on choice and CODE is entered on record
May be entered on main table or a sub-table
Where does lookup code data go?
•If the lookup is a code for something that occurs ONCE per record, it goes into a field on that record.
•If the lookup information could occur more than once you have some choices.
-create a fixed number of fields, each with the same lookup and some way to order them
-create a collection sub-table that can accept multiple rows of data, including the lookup code in each row, linked to one record.
What is a DBMS?
-A piece of software for managing databases and providing access to them.
-A DBMS responds to imperatives ("statements") given by application programs, custom-written or general-purpose, executing on behalf of users.
-Imperatives are written in the database language of the DBMS (e.g. SQL).
-Responses include completion codes, messages and results of queries.
What does a DBMS do?
-creates and destroys variables
-takes note of integrity rules (constraints)
-takes note of authorizations (who is allowed to do what, to what)
-updates variables (honoring constraints and authorisations)
-provides results of queries
What are Environmental Management Information Systems (EMIS)?
•Storage and retrieval of information, such as records and data, needed to support environmental management systems (such as those prescribed by ISO 14001)
•Typically based on a relational database, although spatial databases (such as geographic information systems) are beginning to appear in this context
What is Integrated EMIS?
•Redundancy = noncompliance
•Object oriented approach to the firm
What is EDSS?
•Information systems that help humans make environmental management decisions
•Focused on specific decision problems and decision makers
•Incorporates such active information management operations as modeling, simulation, expert systems and optimization which operate on the data
•Engages spatial data management directly, using geographic information management as the framework
What is integration and Interface?
•Historically, environmental management data and tools have been discrete and disconnected
•This has the effect of preventing actual decision makers from using them
•If we want good decisions, we must make the data and tools accessible to the decision makers
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