DATA MODELING PDF
An Entity-Relationship (ER) diagram provides a graphical model of the things Some data modeling methodologies also include the names of attributes but we. A brief overview of developing a conceptual data model as the first step in creating a This document is an informal introduction to data modeling using the . This chapter discusses the basic concepts in data modeling. It builds At the end of this tutorial, we will have produced a data model, which is commonly.
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Enterprise Architect has extensive support for the data modeling discipline, ranging generating database objects from the UML model or reverse engineering. Breakout groups: Data Modeling Examples. Full group: recap . Source: ppti.info Items 1 - 9 Data Modeling Essentials This page intentionally left blank Data Modeling Essentials Third EditionGraeme C. Simsi.
Figure 1 presents a simple LDM and Figure 2 a simple PDM, both modeling the concept of customers and addresses as well as the relationship between them. Both diagrams apply the Barker notation , summarized below.
Conceptual Data Modelling: an empirical study of expert and novice data modellers
Notice how the PDM shows greater detail, including an associative table required to implement the association as well as the keys needed to maintain the relationships. More on these concepts later.
A PDM should also indicate the data types for the columns, such as integer and char 5. Figure 1. A simple logical data model. Figure 2. A simple physical data model. Data models can be used effectively at both the enterprise level and on projects. Enterprise architects will often create one or more high-level LDMs that depict the data structures that support your enterprise, models typically referred to as enterprise data models or enterprise information models.
Enterprise data models provide information that a project team can use both as a set of constraints as well as important insights into the structure of their system. Project teams will typically create LDMs as a primary analysis artifact when their implementation environment is predominantly procedural in nature, for example they are using structured COBOL as an implementation language.
LDMs are also a good choice when a project is data-oriented in nature, perhaps a data warehouse or reporting system is being developed having said that, experience seems to show that usage-centered approaches appear to work even better. However LDMs are often a poor choice when a project team is using object-oriented or component-based technologies because the developers would rather work with UML diagrams or when the project is not data-oriented in nature.
As Agile Modeling advises, apply the right artifact s for the job. Or, as your grandfather likely advised you, use the right tool for the job.
It's important to note that traditional approaches to Master Data Management MDM will often motivate the creation and maintenance of detailed LDMs, an effort that is rarely justifiable in practice when you consider the total cost of ownership TCO when calculating the return on investment ROI of those sorts of efforts.
When a relational database is used for data storage project teams are best advised to create a PDMs to model its internal schema.
My experience is that a PDM is often one of the critical design artifacts for business application development projects. What About Conceptual Models?
The advantage is that the notation is very simple, something your project stakeholders can quickly grasp, although the disadvantage is that the models become large very quickly.
ORMs enable you to first explore actual data examples instead of simply jumping to a potentially incorrect abstraction — for example Figure 3 examines the relationship between customers and addresses in detail. For more information about ORM, visit www.
Figure 3. A simple Object-Role Model. My experience is that people will capture information in the best place that they know. I sometimes user ORMs to explore the domain with project stakeholders but later replace them with a more traditional artifact such as an LDM, a class diagram, or even a PDM. Not only are they tempted to keep the artifacts that they create but also to invest even more time to enhance the artifacts.
Data Modeling Essentials, Third Edition
Generalizing specialists are more likely than specialists to travel light. Main article: Relational model The relational model was introduced by E. Codd in  as a way to make database management systems more independent of any particular application. It is a mathematical model defined in terms of predicate logic and set theory , and implementations of it have been used by mainframe, midrange and microcomputer systems.
The products that are generally referred to as relational databases in fact implement a model that is only an approximation to the mathematical model defined by Codd. Three key terms are used extensively in relational database models: relations , attributes, and domains.
A relation is a table with columns and rows.
The named columns of the relation are called attributes, and the domain is the set of values the attributes are allowed to take. The basic data structure of the relational model is the table, where information about a particular entity say, an employee is represented in rows also called tuples and columns. Thus, the " relation " in "relational database" refers to the various tables in the database; a relation is a set of tuples.
The columns enumerate the various attributes of the entity the employee's name, address or phone number, for example , and a row is an actual instance of the entity a specific employee that is represented by the relation.
As a result, each tuple of the employee table represents various attributes of a single employee. All relations and, thus, tables in a relational database have to adhere to some basic rules to qualify as relations. First, the ordering of columns is immaterial in a table. Second, there can't be identical tuples or rows in a table. And third, each tuple will contain a single value for each of its attributes. A relational database contains multiple tables, each similar to the one in the "flat" database model.
One of the strengths of the relational model is that, in principle, any value occurring in two different records belonging to the same table or to different tables , implies a relationship among those two records.
Yet, in order to enforce explicit integrity constraints , relationships between records in tables can also be defined explicitly, by identifying or non-identifying parent-child relationships characterized by assigning cardinality , 0 1:M, M:M. Tables can also have a designated single attribute or a set of attributes that can act as a "key", which can be used to uniquely identify each tuple in the table.
A key that can be used to uniquely identify a row in a table is called a primary key. Keys are commonly used to join or combine data from two or more tables.
For example, an Employee table may contain a column named Location which contains a value that matches the key of a Location table. Keys are also critical in the creation of indexes, which facilitate fast retrieval of data from large tables. Any column can be a key, or multiple columns can be grouped together into a compound key.
It is not necessary to define all the keys in advance; a column can be used as a key even if it was not originally intended to be one. A key that has an external, real-world meaning such as a person's name, a book's ISBN , or a car's serial number is sometimes called a "natural" key.
If no natural key is suitable think of the many people named Brown , an arbitrary or surrogate key can be assigned such as by giving employees ID numbers. In practice, most databases have both generated and natural keys, because generated keys can be used internally to create links between rows that cannot break, while natural keys can be used, less reliably, for searches and for integration with other databases.
For example, records in two independently developed databases could be matched up by social security number , except when the social security numbers are incorrect, missing, or have changed. Dimensional model[ edit ] The dimensional model is a specialized adaptation of the relational model used to represent data in data warehouses in a way that data can be easily summarized using online analytical processing, or OLAP queries.
In the dimensional model, a database schema consists of a single large table of facts that are described using dimensions and measures. A dimension provides the context of a fact such as who participated, when and where it happened, and its type and is used in queries to group related facts together. Dimensions tend to be discrete and are often hierarchical; for example, the location might include the building, state, and country.
A measure is a quantity describing the fact, such as revenue. It is important that measures can be meaningfully aggregated—for example, the revenue from different locations can be added together. In an OLAP query, dimensions are chosen and the facts are grouped and aggregated together to create a summary.
The dimensional model is often implemented on top of the relational model using a star schema , consisting of one highly normalized table containing the facts, and surrounding denormalized tables containing each dimension.At this Data Modeling level, no primary or secondary key is defined. Let us explain all these types of data models in DBMS with diagram.
What is a Database Model
When normalized, each piece of data is atomic, or broken into the smallest useful pieces. A PDM should also indicate the data types for the columns, such as integer and char 5. Enterprise data models provide information that a project team can use both as a set of constraints as well as important insights into the structure of their system.
Some post-relational products extend relational systems with non-relational features. Each column lists an attribute of the entity in question, such as price, zip code, or birth date.