Transcript SBA (Stack-Based Approach) and SBQL (Stack

3rd Country Conference, February 2007
SBA (Stack-Based Approach) and
SBQL (Stack-Based Query Language)
by
Prof. Kazimierz Subieta
[email protected]
http://www.ipipan.waw.pl/~subieta
SBA/SBQL pages: http://www.sbql.pl
K.Subieta. Introduction to SBA and SBQL, Slide 1
3rd Country Conference, Feb.2007
What is SBA and SBQL?
• SBA is a conceptual frame for developing O-O
database query/programming languages
– Query languages are programming languages.
• SBQL is a model query language according to SBA.
– It has the same role and meaning as object algebras, but it is
formally sound and much more universal.
• SBA/SBQL deal with various data models and all
imaginable and reasonable query constructs.
• Abstract implementation is the basic paradigm of
formal specification of semantics.
K.Subieta. Introduction to SBA and SBQL, Slide 2
3rd Country Conference, Feb.2007
General architecture of query processing
• Actually, we do not fix the architecture
– It can be similar to SQL or ODMG architectures (serverside query processing, ODBC, ADO or JDBC style, queries
embedded in popular programming languages)
– It can be similar to Oracle PL/SQL (programs integrated
with queries, client-side query processing)
• Shifting query processing and optimization to the
client side
– Lower workload for the server  better overall
performance.
– More flexible for query optimization.
K.Subieta. Introduction to SBA and SBQL, Slide 3
3rd Country Conference, Feb.2007
Software development
environment (editor,
debugger, etc.)
Client
Parser of
queries and programs
Syntactic tree of a query/program
Strong type
checker
Detailed
client-server
architecture
Optimization by
rewriting
Optimization by
indices
Interpreter of queries &
programs
Static ENVS
ENVS
Static QRES
QRES
Local metabase
Volatile (non-shared) objects
Network
Server
Metabase of
persistent
objects
Administration
Transactions
K.Subieta. Introduction to SBA and SBQL, Slide 4
Register
of views
Object
manager
Persistent (shared) objects
Register
of indices
Processing persistent
abstractions (views,
stored procedures,
triggers)
3rd Country Conference, Feb.2007
Object model and database schema
• … are inevitable parts of a query language.
– The application programmer must be aware what the database contains
and how it is organized.
• Usually, an object model and a database schema language are
presented at the beginning of the given specification, c.f. ODMG
• The model involves such concepts as types, classes, interfaces,
joined into a coherent whole as a schema language, c.f. ODL.
– However, the concepts are difficult, especially types.
– Introducing them at the beginning usually results in inconsistencies.
• Hence, we must first understand the semantics of a query
language on the ground of an abstract object store model.
– First, realize what is the semantics of a query language, then define the
corresponding type system.
K.Subieta. Introduction to SBA and SBQL, Slide 5
3rd Country Conference, Feb.2007
SBA semantics of QL-s – general point of view
•
•
•
•
Query - all syntactically correct queries
State - all states (not only database states)
Result - all possible query results.
Semantics of any query is a function that maps
State → Result
• Closure property assumes that a state and a result are
sets of objects
• In SBA a state contains objects (but not only objects)
and a result never contains objects
• Closure property is conceptual nonsense.
K.Subieta. Introduction to SBA and SBQL, Slide 6
3rd Country Conference, Feb.2007
What is State?
• State includes all data or programming features that
can influence the result of some query, in particular:
–
–
–
–
Database state
Local objects used in queries on the client side
Computer and software environment (e.g. date, time)
Libraries, procedures, functions, classes, views, etc.
• State also includes structures that determine the runtime environment of computations.
• In SBA there is one such structure: environment stack
(ENVS) - an extended and modified call stack.
•
state = object store + ENVS
K.Subieta. Introduction to SBA and SBQL, Slide 7
3rd Country Conference, Feb.2007
Is ENVS purely implementation notion?
• No. The environment stack is a conceptual notion.
– ENVS makes it possible to specify precisely the semantics of query
languages, …
– … the mechanisms of classes, roles, static and dynamic inheritance, ...
– … (recursive) procedures, parameter passing, database views,...
– … etc.
• In SBA we deal with ENVS on an abstract level. We are not
interested in its physical implementation.
– Implementation can be different, introducing many optimizations.
– Usually ENVS is a client-side data structure stored in main memory.
• The main roles of ENVS: determining scopes for names and
binding names occurring in queries.
K.Subieta. Introduction to SBA and SBQL, Slide 8
3rd Country Conference, Feb.2007
What is Result?
• Query can return any stored or computed value.
– For instance, query 2+2 returns 4.
• Query can return references (OID, file name, memory
address, etc.).
– For instance, query Person returns references to person
objects.
• Queries can return nested complex values consisting of
atomic values, references, names, structure
constructors and collection constructors.
– SBQL queries never return objects.
– Objects are stored within the object store only.
K.Subieta. Introduction to SBA and SBQL, Slide 9
3rd Country Conference, Feb.2007
Query result stack, QRES
• Temporary and final query results are accumulated on
the query result stack, QRES.
– QRES is a client-side structure stored in main memory.
• QRES must be prepared to store in a single section any
complex query result.
• QRES is not a component of State
– … because the result of a new query does not depend on the
previous QRES state.
• In SBA precise specification of the QRES mechanism
is fundamental.
K.Subieta. Introduction to SBA and SBQL, Slide 10
3rd Country Conference, Feb.2007
Example of QRES state
top
15
the only visible stack section
i17
struct{ x(i61), y(i93) }
bag{
bottom
invisible stack sections
struct{ n("Doe"), s(i9)},
struct{ n("Poe"), s(i14)},
struct{ n("Lee" ), s(i18)}}
K.Subieta. Introduction to SBA and SBQL, Slide 11
3rd Country Conference, Feb.2007
Total internal identification
• Each database or program entity, which could be separately
retrieved, updated, inserted, deleted, authorized, indexed,
protected, locked, should possess a unique internal identifier.
– We are not interested in the form and meaning of internal identifiers.
– Unique internal identifiers should be assigned to all components of
objects, including atomic ones.
– The principle makes it possible to make references and pointers to all
possible entities, thus to avoid conceptual problems with binding,
scoping, updating, deleting, parameter passing, and other
functionalities that require references as query primitives.
• ODMG does not follow the idea.
– ODMG „literals” (components of objects) have no identifiers.
– I consider this a fundamental conceptual flaw.
K.Subieta. Introduction to SBA and SBQL, Slide 12
3rd Country Conference, Feb.2007
Object relativism
• If some object O1 can be defined, then object O2 having O1 as a
component can also be defined.
– No limitations concerning the number of hierarchy levels of objects.
– Objects on any hierarchy level should be treated uniformly.
– An atomic object (having no attributes) should be allowed as a regular
data structure.
• Object relativism implies the relativism of corresponding query
capabilities.
– There is no need for attributes, sub-attributes, etc. - all are objects too.
• The idea radically reduces a database model, cuts the size of
specification of query languages, the size of implementation, and
the size of documentation.
– It much supports query optimization and strong typing.
K.Subieta. Introduction to SBA and SBQL, Slide 13
3rd Country Conference, Feb.2007
Abstract Object Store Models
• A component of State is an object store.
– To define the semantics of a query language we have to define an
object store precisely, but on the abstract level.
• Because various object models introduce a lot of incompatible
notions, SBA assumes some family of object store models which
are enumerated M0, M1, M2 and M3.
– M0 covers relational, nested-relational and XML-oriented databases.
M0 assumes hierarchical objects and binary links between objects.
– Advanced store models introduce classes and static inheritance (M1),
object roles and dynamic inheritance (M2), and encapsulation (M3).
– All the models are served by SBQL.
• These store models are pivots - they can be extended and
modified, depending on features that one would like to cover.
K.Subieta. Introduction to SBA and SBQL, Slide 14
3rd Country Conference, Feb.2007
Notions common to store models
1. Internal object identifier (OID)
–
–
–
Uniquely identifies an object in the store.
Assigned automatically, no external meaning.
Used as a reference or a pointer to an object.
2. External object name
–
–
–
Usually bears some external semantics of an object, e.g. Person,
Customer.
Explicitly assigned by a database designer, programmer, etc.
It is usually not unique, e.g. many objects named Person.
3. Atomic object value
–
–
–
–
Cannot be subdivided into smaller parts
E.g. 2, 3.14, “Doe”, “Hello, World!”.
The size is not constrained – from 1 bit to gigabytes.
So far we neglect types (we deal with types later).
K.Subieta. Introduction to SBA and SBQL, Slide 15
3rd Country Conference, Feb.2007
M0 : Complex Objects and Pointer Links
I - a set of internal identifiers
N - a set of external names
V - a set of atomic values
< i, n, φ >
object
object ID
object name
< i, n, v > - atomic object
< i1, n, i2 > - pointer object
< i, n, T > - complex object,
T is a set of objects
R  I – start identifiers
object value
• No record, tuple, array, set, etc. constructors in the model:
essentially all of them are collections of objects.
• External names are not unique: modeling collections (bags).
• Uniform treatment of relational, nested relational, etc.
databases.
K.Subieta. Introduction to SBA and SBQL, Slide 16
3rd Country Conference, Feb.2007
M0 object store - example
Objects
< i1, Emp, { < i2, name, ”Doe” >,
< i3, sal, 2500 >,
< i4, worksIn, i17 > } >
< i5, Emp, { < i6, name, ”Poe” >,
< i7, sal, 2000 >,
< i8, worksIn, i22> } >
< i9, Emp, { < i10, name, ”Lee” >,
< i11, sal, 900 >,
< i12, address, { <i13, city, “Rome” >,
<i14, street, “Boogie” >,
<i15, house#, 13 > } >,
< i16, worksIn, i22 > } >
< i17, Dept, { <i18, dname, ”Trade” >,
< i19, loc, “Paris” >,
< i20, loc, “London” >,
< i21, employs, i1 > } >
< i22, Dept, { < i23, dname, ”Ads” >,
< i24, loc, “Rome” >,
< i25, employs, i5 >,
< i26, employs, i9 > } >
Start identifiers i1, i5, i9, i17, i22
K.Subieta. Introduction to SBA and SBQL, Slide 17
3rd Country Conference, Feb.2007
M0 object store – graphical view
i1 Emp
i5 Emp
i9 Emp
i2 name ”Doe”
i6 name ”Poe”
i10 name ”Lee”
i3 sal 2500
i7 sal 2000
i11 sal 900
i4 worksIn
i8 worksIn
i12 address
i13 city ”Rome”
i14 street ”Boogie”
i15 house# 13
i16 worksIn
i17 Dept
i22 Dept
i18 dname ”Trade”
i23 dname ”Ads”
i19 loc ”Paris”
i24 loc ”Rome”
i20 loc ”Rome”
i25 employs
i21 employs
i26 employs
K.Subieta. Introduction to SBA and SBQL, Slide 18
3rd Country Conference, Feb.2007
A relational database in M0
Relational schema:
Emp( name, sal, worksIn )
Model M0:
Relation: Emp
Objects:
< i1 , Emp, { < i2, name, ” Doe” >,
< i3, sal, 2500 >,
< i4, worksIn, ” Production” > } >,
name
Doe
Poe
Lee
sal
2500
2000
2000
worksIn
Production
Sales
Sales
< i5 , Emp, { < i6, name, ” Poe” >,
< i7, sal, 2000 >,
< i8, worksIn, ” Sales” > } >,
< i9 , Emp, { < i10, name, ” Lee” >,
< i11, sal, 2000 >,
< i12, worksIn, ” Sales” > } >
Start identifiers: i1 , i5 , i9
• A similar mapping can be applied to hierarchical DB, nested
relational DB, XML, RDF, …
K.Subieta. Introduction to SBA and SBQL, Slide 19
3rd Country Conference, Feb.2007
Environment Stack, ENVS
• ENVS is also known as call stack.
• For query processing we modified and generalized it:
– ENVS is used to binding objects that are stored at a server, hence
ENVS contains references to objects rather than object values.
– The same object can be referenced from different stack sections.
– For collections the binding is macroscopic, for instance, if Emp is
bound, the binding returns many references.
• In PLs the stack has usually two incarnations: static (compile
time) and dynamic (run-time).
• Because database objects are always dynamically bound, some
properties of a static stack must be shifted to a dynamic stack.
– We deal with the static stack when we consider strong typing.
• Besides classical roles of the stack, SBA provides many new
roles of it, in particular, processing non-algebraic operators.
K.Subieta. Introduction to SBA and SBQL, Slide 20
3rd Country Conference, Feb.2007
Naming, scoping, binding
• SBA is based on the naming, scoping and binding paradigm:
• Every name occurring in a query is bound to run time program
or database entities, according to the actual scope for the name.
• Binding is substituting a name occurring in a query by a runtime program entity (or entities).
• This concerns all names, in particular:
– Names of persistent or volatile objects, subobjects (attributes),
pointers, procedures, functions, methods, views, parameters.
– Names of entities from the computer or software environment
– Any auxiliary names that are defined and used in queries
• ENVS presents a universal scoping and binding mechanism.
– No name occurring in a query can be bound otherwise.
• ENVS stores binders, i.e. pairs n(r), where n  N, r  Result.
K.Subieta. Introduction to SBA and SBQL, Slide 21
3rd Country Conference, Feb.2007
Opening a new section of ENVS (1)
• In PLs opening a new scope on ENVS is caused by entering a
new procedure (function, method) or entering a new block.
– Respectively, removing the scope is performed when the control leaves
the body of the procedure/block.
• To these classical situations we add a new one.
– It is the essence of SBA. The idea is that some query operators (called
non-algebraic) behave on the stack similarly to program blocks.
– In the SBQL query:
Emp where ( name = “Poe” and sal > 1000 )
the part ( name = “Poe” and sal > 1000 ) behaves as a program block
executed in an environment consisting of the interior of an Emp object.
• Binding concerns also names name and sal.
– Hence, we push on ENVS a section with the interior of the currently
processed Emp object (next slide).
K.Subieta. Introduction to SBA and SBQL, Slide 22
3rd Country Conference, Feb.2007
Opening a new section of ENVS (2)
condition
Emp
where
binding
(name = ”Poe” and sal > 1000)
binding
name(i10) sal(i11)
address(i12) worksIn(i16)
Emp(i1) Emp(i5) Emp(i9)
Dept(i17) Dept(i22)
Initial ENVS state.
bind( Emp ) = {i1, i5, i9}
K.Subieta. Introduction to SBA and SBQL, Slide 23
Interior of the
3-rd object Emp
Emp(i1) Emp(i5) Emp(i9)
Dept(i17) Dept(i22)
ENVS during evaluation of the condition
for the third object Emp.
bind( name ) = i10; bind( sal ) = i11
3rd Country Conference, Feb.2007
Function nested – computing object’s interior
• Function nested acts on an object reference and returns its
interior as a set of binders. For instance:
i9 Emp
i10 name ”Lee”
i11 sal 900
i12 address
i13 city ”Rome”
i14 street ”Boogie”
i15 house# 13
i16 worksIn
nested( i9 ) = { name( i10 ), sal( i11 ), address( i12 ), worksIn( i16 ) }
• The result of nested is then pushed at ENVS.
K.Subieta. Introduction to SBA and SBQL, Slide 24
3rd Country Conference, Feb.2007
Generalization of function nested
• In general, it can be applied to any element of Result.
– For a complex object <i, n, { <i1, n1,...>, <i2, n2,...>, ... , <ik, nk> }>
it holds: nested( i ) = { n1(i1), n2(i2), ... , nk(ik) }
• The case is illustrated on the previous slide.
– If i is an identifier of a pointer object <i, n, i1>, and the object store
contains the object <i1, n1, ... >, then nested( i ) = { n1(i1) }
• This accomplishes navigation according to a pointer.
– For a binder n(x) holds: nested( n(x) ) = { n(x) }
• According to understanding of auxiliary names introduced in queries.
– For a structure nested returns the union of the results of the nested
function applied for elements of the structure:
nested( struct{ x1, x2, ... } ) = nested(x1)  nested(x2)  ...
• For other arguments nested returns the empty set.
K.Subieta. Introduction to SBA and SBQL, Slide 25
3rd Country Conference, Feb.2007
Definition of Result for SBQL
•
•
•
•
Any atomic value belongs to Result.
Any reference (OID) belongs to Result.
If x belongs to Result, then any binder n(x) belongs to Result.
If x1, x2, x3, ... belong to Result, then the structure
struct{ x1, x2, x3, ... } belongs to Result.
– In contrast to typical structures, we do not assume that all elements of
a structure must be named.
– Empty structures are not allowed.
• If x1, x2, x3, ... belong to Result, then bag bag{x1, x2, x3, ... } and
sequence sequence{x1, x2, x3, ... } belong to Result.
– bag and sequence are collection constructors.
– Other collection constructors are possible.
K.Subieta. Introduction to SBA and SBQL, Slide 26
3rd Country Conference, Feb.2007
Summing up: what we have defined so far?
• We know precisely what is an object store, atomic object,
complex object, pointer object and collection.
• We know precisely what is the construction of an environment
stack ENVS, what it is for, what is binding, and how a new
section on the stack is constructed (binders, function nested).
• We know precisely what is a query result and a query result
stack QRES.
• Abstract implementation of a query language has the form of
the recursive procedure eval (evaluation of a query).
• This is all the semantic equipment to define SBQL and its
abstract implementation for the M0 store model.
• For details see http://www.sbql.pl
K.Subieta. Introduction to SBA and SBQL, Slide 27
3rd Country Conference, Feb.2007
Examples of SBQL queries for M0
– Get references of departments for employee named Doe:
(Emp where name = “Doe”).worksIn.Dept
– Get names of departments together with their average salaries:
(Dept join avg(employs.Emp.sal) as avgsal) . (dname, avgsal)
– Names and cities for employees working in the department managed by
Kim:
(Dept where (boss.Emp.name) = “Kim”).employs.Emp.
(name, if exists(Address) then Address.city else “No address”)
– Get departments employing a professional for any job in the company.
Dept where distinct(Emp.job) as j (employs.Emp (j = job))
– Names and salaries of employees earning more than their bosses.
(Emp where sal > (worksIn.Dept.boss.Emp.sal)).(name, sal)
K.Subieta. Introduction to SBA and SBQL, Slide 28
3rd Country Conference, Feb.2007
M1 : Classes and static inheritance
• Classes, methods and inheritance require extension of M0.
• Classes have two incarnations: as pieces of a source code and as
run-time database entities.
– Usually programming languages deal with classes as second-class
citizens, i.e. in the source code only.
– In our model we are (so far) not interested in this point of view.
• We deal with them when we consider static binding and strong typing.
– In the M1 store model classes are first class entities storing invariant
properties of their objects, i.e. methods (but not only).
• Hence in our model classes are objects too, connected with their
member objects by a special relationship.
• Classes are also connected with classes by another relationship
know as inheritance.
K.Subieta. Introduction to SBA and SBQL, Slide 29
3rd Country Conference, Feb.2007
Classes as objects in M1
i40 PersonClass
i41 age (...code...)
...
inherits from
i50 EmpClass
member of
i51 changeSal (...code...)
i52 netSal (...code...)
...
i1 Person
member of
i2 name ”Doe”
...
i5 Emp
i9 Emp
i6 name ”Poe”
i10 name ”Lee”
i7 sal 2000
i11 sal 900
i8 worksIn
i16 worksIn
...
K.Subieta. Introduction to SBA and SBQL, Slide 30
member of
i22
...
i33
3rd Country Conference, Feb.2007
SBQL semantics for M1
• Changes concern only ENVS and non-algebraic operators
– When a non-algebraic operator processes an object <i, …>, which is a
member of a class <iC1, …>, which inherits from a class <iC2, …>, etc.
then the ENVS is augmented (starting from the top) by nested(i),
nested(iC1), nested(iC2), …up to the most general class.
– When a non-algebraic operator finishes processing the object <i, …>,
all these sections are removed from ENVS.
During processing the object <i, …>
nested( i )
Before processing
the object <i, …>
nested(iC1)
nested (iC2)
After processing
the object <i, …>
…..
Previous ENVS state
K.Subieta. Introduction to SBA and SBQL, Slide 31
Previous ENVS state
Previous ENVS state
3rd Country Conference, Feb.2007
Example: Processing an object in M1
(Emp where name = “Poe”) . (name, netSal, age)
• ENVS during processing the subquery after the dot:
nested(i5) - internals of the currently
processed Poe’s object
nested (i50) – internals of EmpClass
nested (i40) – internals of PersonClass
Binders to database objects
K.Subieta. Introduction to SBA and SBQL, Slide 32
name(i6) sal(i7) worksIn(i8) …
changeSal(i51) netSal(i52) ...
Sections
pushed by
the dot
age(i41) ...
…
Person(i1) ... Emp(i5) Emp(i9) ..
...
3rd Country Conference, Feb.2007
Some peculiarities of M1
• Binding and processing methods:
– Invocation of a method means that a new section (activation record) is
additionally pushed at top of ENVS.
– The section contains parameters of the method (evaluated previously),
its local environment and a return track.
– Some peculiarities connected with encapsulation.
• A problem - multiple inheritance:
– M1 allows for multiple inheritance, but in case of name conflict there
is no solution.
• This is a general problem, not specific to M1.
• Another problem - collections:
– They violate object-oriented principles such as substitutability and
open-close (reuse, conceptual continuation).
– Possible solutions require specific extensions of M1.
K.Subieta. Introduction to SBA and SBQL, Slide 33
3rd Country Conference, Feb.2007
Examples of SBQL queries for M1 - schema
Person[0..*]
name
birthYear
Address [0..1]
city
street
house#
UML-like, but:
• Cardinalities assigned to all database entities
• Nested classes
• Pointers rather than association roles
age()
worksIn
Emp[0..*]
e#
manages[0..1]
job[1..*]
sal[0..1]
changeSal(newSal)
netSal( )
K.Subieta. Introduction to SBA and SBQL, Slide 34
Dept[0..*]
employs[1..*] d#
dname
boss loc[1..*]
budget()
3rd Country Conference, Feb.2007
Examples of SBQL queries for M1
– Get names of departments and the average age of their employees
(inheritance of the method age).
Dept . (dname, avg(employs.Emp.age))
– Get employees that for sure live in the cities where their departments
are located (inheritance of Address).
Emp where  Address as a ( (worksIn.Dept.loc) as l (a.city = l))
– For each employee get name and the percent of the annual budget of
his/her department that is consumed by his/her sal.
Emp . (name, (((if exists(sal) then sal else 0) as s).
((s * 12 * 100)/(worksIn.Dept.budget)))
– For each person having no salary give the minimal salary in his/her
department.
for each (Emp where not exists(sal)) as e do
e.changeSal( min(e.works_in.Dept.employs.Emp.sal) );
K.Subieta. Introduction to SBA and SBQL, Slide 35
3rd Country Conference, Feb.2007
M2: Dynamic roles and dynamic inheritance
• The object model with dynamic object roles removes essential
conceptual drawbacks of the classical static inheritance.
– The idea is that an object during its life can acquire and lose its roles
without changing its identity.
– Object’s business semantics depends on a currently considered role.
• SBQL is the first (and only) QL dealing with dynamic roles.
– Dynamic object roles and dynamic inheritance require extension of
M1 and extension of the semantics of non-algebraic operators.
Person
Employee
Patient
Student
Student
K.Subieta. Introduction to SBA and SBQL, Slide 36
Tax-payer
Club-member
Dog-owner
3rd Country Conference, Feb.2007
Example of the M2 store model
i50 EmpClass
i51 changeSal (...code...)
i40 PersonClass
i60 StudentClass
i41 age (...code...)
i61 avgScore (...code...)
i52 netSal (...code...)
.............
.............
.............
i1
Person
i4
Person
i7
Person
i2 name ”Doe”
i5 name ”Poe”
i8 name ”Lee”
i3 born 1948
i6 born 1975
i9 born 1951
is member of
i13 Emp
i16 Emp
i19
inherits from
i14 sal 2500
i17 sal 1500
i20 studentNo 223344
dynamically
inherits from
i15 worksIn
i18 worksIn
i21 faculty ”Physics”
K.Subieta. Introduction to SBA and SBQL, Slide 37
i127
Student
i128
3rd Country Conference, Feb.2007
SBQL semantics for M2
• Changes concern only ENVS and non-algebraic operators
– The order of sections of roles and classes on ENVS is determined by a
simple rule (c.f. full description of SBA/SBQL).
– Some new operators dealing with roles (dynamic cast, has role).
(Emp where name = ”Lee”) . (sal, born, age)
Sections
pushed by
the dot
sal(i17) worksIn(i18)
Properties of the currently processed
Emp role
changeSal(i51) netSal(i52 ) ...
Properties of the EmpClass
name(i8) born(i9)
Properties of the Person super-role of
the Emp role
age(i41) ...
Properties of the PersonClass
.........
Person(i1) Person(i4) Person(i7)
Emp(i13) Emp(i16) Student(i19) ...
.........
K.Subieta. Introduction to SBA and SBQL, Slide 38
Database section
3rd Country Conference, Feb.2007
Examples of SBQL queries for M2 - schema
K.Subieta. Introduction to SBA and SBQL, Slide 39
3rd Country Conference, Feb.2007
Examples of SBQL queries for M2
– Get employees older than 60 who live in Warsaw (dynamic inheritance
of the attribute Address and static inheritance of the method age).
Emp where age > 60 and Address (city = “Warsaw”)
– For each person get name and the sum of all the incomings (salary and
scholarships).
(Person as p).
(p.name, sum(bag(0, ((Student)p).scholarship, ((Emp)p).sal)))
– Get students who live in the same city as the city of their school.
Student where Address (city = (studiesAt.School.city))
– Get name, faculty and school name for each person studying at two or
more faculties.
(((Person as p) join ((((Student)p) group as s))) where count(s) ≥ 2).
(p.name, s.(faculty, (studiesAt.School.name)))
K.Subieta. Introduction to SBA and SBQL, Slide 40
3rd Country Conference, Feb.2007
Conclusions
• To make a high quality standard for object-oriented databases,
the specification of semantics is the must, …
– …to avoid the fate of SQL-99 and ODMG standards, perceived as
loose recommendations rather than technical specifications.
• SBA offers the unique method of query languages’ construction
and semantic specification.
– SBA is a holistic database theory, it doesn’t give up any (even the most
advanced) feature of current practical O-O database QL/PL.
– Efficiency has been proven by several implementations.
• The new standardization activity should not trust the currently
well-known concepts concerning O-O query languages.
– IMO: limited, imprecise, immature, inconsistent.
– Following them  standard’s qualities will be among nice wishes.
• So far SBA has no serious competitive approach.
K.Subieta. Introduction to SBA and SBQL, Slide 41
3rd Country Conference, Feb.2007