Impact Factor: ISRA (India) = 4.971 ISI (Dubai, UAE) = 0.829 GIF (Australia) = 0.564 JIF = 1.500 SIS (USA) = 0.912 РИНЦ (Russia) = 0.126 ESJI (KZ) = 8.997 SJIF (Morocco) = 5.667 ICV (Poland) = 6.630 PIF (India) = 1.940 IBI (India) = 4.260 OAJI (USA) = 0.350 Philadelphia, USA 391
to decompose data streams) until functions can be split
into parts.
Construction of specifications of elementary
processes (at the level of algorithms).
If necessary - making changes to the DFD of any
levels as the details of the requirements are clarified.
The result of completing all of these stages is a
ready-made model of the functional requirements of
the system and a clear understanding of the structure
of the subject area. At the end of this stage, you can
proceed to building the data model.
ESSENCE-CONNECTION DIAGRAMS
One of the most commonly used tools for
developing data models are Entity-Relationship
Diagrams (ERDs). ERDs provide a standard way to
define data and the relationships between them. With
their help, the detailing of the data stores of the
designed system is carried out, the system components
are determined, the ways of their interaction,
including the identification of objects important for
the subject area (entities), the properties of these
objects (attributes) and their relations with other
objects (links).
This notation was introduced by Chen and was
further developed by Barker. These diagramming
techniques are used to design relational databases.
An entity is a set of instances of real or abstract
objects (people, events, states, ideas, objects, etc.) that
have common attributes or characters. Any system
object can be represented by only one entity, which
must be uniquely identified. In this case, the name of
the entity should reflect the type or class of the object,
and not its specific instance (for example, PATIENT,
not KIM N.I.).
An
independent
entity
represents
the
independent data that is always present in the system
and the relationship. other entities may or may not
exist.
A dependent entity represents data that is
dependent on other entities in the system. Therefore,
it must always have relationships with other entities.
An associated entity represents data that is
associated with a relationship between two or more
entities (see many-to-many relationships below).
A relationship in its most general form is a
relationship between two or more entities. Verb
groups are used to name relationships (has, can own,
defines).
An unconstrained (mandatory) relationship is an
unconditional relationship, that is, a relationship that
always exists as long as there are related entities.
A constrained (optional) relationship is a
conditional relationship between entities.
A substantially constrained relationship is used
when the respective entities are interdependent in the
system.
Relationships
are
used
to
identify
the
requirements by which entities are involved in
relationships. Each relationship connects an entity and
a relationship and can only be directed from
relationship to entity.
The value of a link characterizes its type and, as
a rule, is selected from the following set:
{"0 or 1", "0 or more", "1", "1 or more", "p: q"} A pair of relationship values belonging to the
same relationship determines the type of this
relationship. The following types of relationships are
used:
1 * 1 (one-to-one); 1 * N (one-to-many); N * M (many-to-many). Relationships of this type are used in the early
design stages to clarify the situation. In the future,
each of these relations must be converted into a
combination of relations of types 1.
2 (possibly with the addition of auxiliary
associative entities and the introduction of new
relationships).
Demonstrating the relationship between the
objects of a medical organization (polyclinic).
According to this diagram, each doctor treats one or
more patients. In addition, each patient may or may
not be treated by one or more physicians. Each doctor
conducts an outpatient appointment for which patients
are registered (assigned). In the process of examining
patients at an outpatient appointment, the doctor forms
epicrises that affect the diagnosis. Every diagnosis for
a patient must have an author - a doctor who is
responsible for making the decision.
Each entity has one or more attributes that
uniquely identify each instance of the entity.
Moreover, any attribute can be defined as key.
Entity drill-down is accomplished using attribute
diagrams that expose the attributes associated with an
entity. An attribute diagram consists of a drillable
entity, associated attributes, and domains that describe
the attribute value ranges. In the diagram, each
attribute is represented as a relationship between the
entity and the corresponding domain, which is a
graphical representation of the set of possible attribute
values. All attribute links have meaning at their end.
The attribute name underscore is used to identify a key
attribute.
An entity can be split and represented as two or
more entity-categories, each of which has common
attributes and / or relationships. The entity split into
categories was called the general entity (at
intermediate levels of decomposition, the same entity
can be both a general entity and an entity-category).
To demonstrate the decomposition of an entity
into categories, categorization diagrams are used.
Such a diagram contains a general entity, two or more
entity-categories, and a special node - a discriminator,
which describes how entities are decomposed.
The ER-approach was further developed in the
works of Barker, who proposed an original notation
that made it possible to integrate the model description
tools proposed by Chen at the top level. There is only